Take a penny...
I have always wondered how the "give a penny, take a penny" system works. Do you take a penny to make up the change when you pay for something? and add chnage you cant be bothered to have in your wallet in there? This might seem quit pointless but I can't find any references to it on the internet and I heard it on The Simpsons recently when homer becomes a cop and Apu says you desearve to take a penny but that makes it sound like you just take money???
the concept is for people who do not like change (me included) to leave the excess change there(normally anything silver (5 cents +) vanishes into the merchants pocket though) this allows the people who are short changed to be able to make up the difference and not have to leave the store with nothing when they were short a few pennies.
If you want more explination Wolf then wiki it!