I'm not exactly sure of the sense of trying to return money in small denominations or any singular amount of money unless it was part of the contents of another package. Unless that owner is plainly obvious.
How do you actually determine the rightful owner of something that almost everyone would have on them from day to day? Ask them for the serial number?
I can see it for a large amount that the authorities could then ask the person exactly how much they lost but after working at the mall I know people that will come to lost and found every few days and ask if a ten, twenty, etc. was found.
I also find the instance of the authorities charging the finding party who honestly turned something in a percentage to claim it after the owner failed to do so pretty crappy!