Pennies From Heaven, Or At Least Gas Stations

Last I heard, there were about 300 million people in the United States. According to CoinStar those 300 million people have about $10.5 billion in loose change laying around. Some of it ends up in those "Take a penny, leave a penny" trays at the local convenience store, supermarket, gas station, etc. I decided to find out just how much money I could collect from cleaning out these trays.

First, some ground rules:

1. Get permission from the person at the register before emptying the tray. Explain it's for an "Internet experiment."
   
2. Leave at least 4 pennies, so the next person who needs to complete a transaction will have something to work with.
3. Document the results for all to see.

I'll have to work out the details as I go along. For instance, would this be considered taxable income? How many retailers will deny my request? Should I go back to the same location multiple times, or only empty each tray once?

While I don't expect to get "rich" from this little endeavor, I'm hoping it will at least pay for a cup of coffee now and then, and perhaps spark some interesting dialog here. Let me know what you think!