Raise your right hand, look me squarely in the eye, and tell me this: Do you know how much sales tax you are supposed to pay on a $48.43 supermarket order in Washington? In Maryland? In Virginia?

If you answered "Yes" three times, you're smarter than some of the tax collectors and supermarket employees I've been talking to this week.

The three sales tax laws differ so much that I find myself looking at my notes and saying, "Bill, this can't be right. You must have misunderstood what they told you."

Virginia's 4 per cent sales tax law applies to both food and nonfood items. From 1 cent to 14 cents, there is no tax; from 15 to 34 cents the tax is 1 cent; from 35 to 59 cents the tax is 2 cents; from 60 to 84 cents the tax is 3 cents; from 85 to $1.14 the tax is 4 cents. thereafter, add 4 cents for each additional dollar. The "break points" remain the same.

Maryland charges a 5 per cent sales tax, but food purchased for preparation at home is not taxed.

However, candy and soda pop are not considered food, so they are taxed. Restaurant meals are also taxed, except that those under $1 are not, e.g.: If one sandwich costs 99 cents, there is no tax, but two 99-cent sandwiches cost $1.98 plus 10 cents in tax.

Maryland's break points are as follows: Up to 19 cents, no tax; on 20 cents the tax is 1 cent, on 21 to 40 cents is 2 cents, on 41 to 60 cents it is 3 cents; on 61 to 80 cents it is 4 cents; on 81 cents to $1 it is 5 cents; on $1.01 to $1.20 it is 6 cents and thereafter the cycle is repeated.

The District of Columbia has only five sales taxes thus far, but given time the City Council may decree some others. We have a 2 per cent sales tax, a 6 per cent tax, an 8 per cent tax, a 10 per cent tax and a 12 per cent tax.

The 2 per cent tax is on items sold through vending machines. It is usually paid by the vendor. The consumer doesn't have to worry about it.

The 6 per cent tax is the one that applies to "everything else."

The 8 per cent tax is levied on food and alcohol served in restaurants.

The 10 per cent tax applies to hotel and motel rooms.

The 12 per cent tax applies to "storage" and is usually known as the "parking tax."

The District's sales tax does not apply to food purchased for consumption at home but does apply to some "prepared" food sold in supermarkets and delicatessens. I will not attempt to explain what is taxable and what is not because I cannot get the hand of the various distinctions that are made.

For example: Cooked roast beef sold at the deli counter of a D.C. supermarket is not taxed, but a barbeque

If you can keep all this straight, you are a certified genius.

Giant Food's computer may be able to remember the break points on the District's various sales tax rates, but I doubt that many humans can. The 6 per cent schedule goes like this: 1 to 17 cents, 1 cent; 18 to 35 cents, 2 cents; 36 to 53 cents, 3 cents; 54 to 71 cents, 4 cents; 72 to 89 cents, 5 cents; 90 cents to $1.12, 6 cents; $1.13 to $1.17, 7 cents; etc.

The 8 per cent schedule is entirely different. On a purchase of 12 cents or less, there is no tax; from 13 to 16 cents, it is 1 cent; 17 to 27 cents, 2 cents; 28 to 39 cents, 3 cents; 40 to 50 cents, 4 cents; 51 to 62 cents, 5 cents; 63 to 75 cents, 6 cents; 76 to 90 cents, 7 cents; 91 cents to $1.12, 8 cents, etc.

Some restaurants "round off" the sales tax. On the theory that customers dislike getting pennies in change, they just raise the tax to the next higher nickel. Rounding off is not permitted under the law.

The 10 per cent hotel tax is the only one I can understand. It is a true 10 per cent of the bill, with fractions breaking for the customer if they are under a half-cent.

The 12 per cent parking tax is such an abomination I'm glad there is no room to tell you where the break points are on that one. Besides, you wouldn't believe me if I did.

With so many of us whizzing around the Beltway or across state lines to do our shopping these days, perhaps you'd better clip and save this column for future reference. I don't think I could write it a second time without going bananas.