When you purchase something, and get two cent in change, you put that change in a litle box located on the counter top at the store.
Next customer that comes along is just two cents short for the item they wish to purchase. They are welcome to take the amount of change they need out of the GAP, TAP box.
So each time you donate your pennies to GAP, TAP... you're paying for a stranger's goods.
These GAP, TAP boxes can be found at any store. Most commonly at 7-Eleven, Taco Bell, McDonald's and Rite-Aid.