Penny candy disappeared years ago and inflation has turned our dull copper discs into the leftover garbage of consumerism. So each evening millions of people practice the monotonous ritual of culling the dark change from the shiny. Into countless flowerpots, mugs and jars go Lincoln head pennies, to be dragged to the bank "sometime."Yet if a penny saved is no longer a penny earned, at least a penny collected might be a penny sold at many times its face value years later. Start by pruchasing an 89-cent Whitman coin folder (sold by coin dealers; look in the Yellow Pages) and each evening fill the empty slots under labels like "1921S." Except for raer coins, it won't be long before the folders fill up. However, there is a difference between investing and collecting. Mark Holloway of Woodward/Lothrop's downtown coin shop says: "A hobby is supposed to be fun. The people who think of money first and the hobby second are called investors." So even elaborate penny collections won't put the kids through college 20 years from now, but chances are you'll begin looking at the nickels, dimes and quarters in your change, and those collections just might put the children in the classroom (or send you to Tahiti).