It's Cyber Monday, that time of year when millions of us will rush to online retailers like Amazon in hopes of scoring a great post-Thanksgiving deal. But if you live in one of a handful of states, your "savings" will be affected by the collection of online sales taxes — an issue that has grown increasingly controversial as e-commerce has become a huge part of holiday sales. This weekend alone, 103 million people shopped online, spending $4.4 billion between Thanksgiving Day and Black Friday, according to the National Retail Federation.

What you'll pay in sales taxes often depends on a number of factors, including where you live, where your seller is based and — not surprisingly — the outcome of a years-long legislative slog in Congress. As you complete your holiday shopping list, here's what you need to get up to speed.

Most of us are familiar with the sales taxes we pay when we visit restaurants and shopping malls. But things get complicated when the Internet comes into play. A 1992 Supreme Court decision in Quill v. North Dakota basically set up the rules we have today: Unless an online business actually has a physical presence of some kind in a given state, it isn't required to collect that state's sales tax.

This is how, for a long time, many of us effectively got a tax break whenever we shopped online. Technically, we're all still on the tax hook for transactions made over the Internet no matter where we live, but it turns out to be a really difficult obligation to enforce. As a result, many consumers simply get to pocket the difference.

Understandably, a lot of brick-and-mortar stores were upset by that, because it tended to give online storefronts an advantage. Cities and states, too, were disappointed because they were missing out on tens of billions of dollars a year in potential tax revenue.

In response, some states passed laws aimed at closing that gap, in spite of the federal ruling in Quill. Colorado, for instance, approved a bill that forced Internet businesses to tally up all their sales and then send those figures to both the state and to customers so that the state could go after its residents and make sure they paid what they owed. By changing the requirement on businesses from a collection requirement to a reporting requirement, Colorado essentially circumvented the Quill decision. But court challenges to laws such as these keep cropping up from time to time; in March, Colorado suffered a setback when the Supreme Court allowed a suit against the state's online tax law to continue in a lower court. The law has been temporarily suspended while the litigation moves ahead.

Scenes like the one in Colorado are playing out all across the country, with varying results. That's why many in Congress want to pass a national law that would clear things up. Lawmakers appear generally supportive of letting states collect the taxes they're owed, but the political fight over how that should actually happen is surprisingly divisive.

What's at stake is both how much consumers should be taxed, and which states should benefit from the revenues. On the first question, there are generally two opposing views: (A) Consumers should be taxed based on where they live or (B) consumers should be taxed based on the location of their seller. Forty-two percent of respondents in a recent poll supported A, while 31 percent said B.

As for which state should benefit from online sales taxes — the buyer's or the seller's — 45 percent said the revenue should flow to consumers' home state, not the state where the seller is based.

Competing bills in Congress offer different flavors of these positions. Though there's plenty of talk of bipartisanship in these proceedings, partly what makes the whole thing interesting is the internal split among Republicans over the issue. Anti-tax conservatives oppose the legislation, while others say it would restore a level playing field between online retailers and mom-and-pop, brick-and-mortar stores.

None of this legislation seems poised to move in the short term, because it would all have to go through Rep. Bob Goodlatte (R-Va.), the chair of the House Judiciary Committee, who has argued for an online tax rate that's based on where the seller is. Other GOP lawmakers, such as Rep. Jason Chaffetz (R-Utah), have proposed a bill that opts for the buyer-based alternative.

Until Congress reaches a consensus, or the Supreme Court takes a case that allows it to revisit and overturn its decision in Quill, the nation will continue to be governed by a patchwork of state online tax laws. Keep in mind that if you're buying from an online retailer that has a physical presence in your state, such as a warehouse, chances are you will be charged sales tax by the company even if the state has no specific rules on online sales taxes.