I thought the universal rule of finders keepers trumped the law, I guess not.
Can you go to jail for finding money?
Yes, if you make no effort to find the rightful owner or turn it into the police, it is a crime (in CA, PC 485). This goes for money and anything else of value… In practical use, if it's a dime and there is nobody around, you won't be arrested or prosecuted for pocketing it.