Well you could call the bank, and give the money back.

Which would open up a case to have the machine checked and then would most likely point to the last tech who worked with the machine. That may get the person fired or get a slap on the wrist, you need to consider this. Were you the only person the machine did this for? Or was it malfunctioning like that the entire day.

I know this is your life and someone made a mistake which caused the machine to give you extra money or possible the bills were so new that they got stuck together.

Seriously, just keep the money dude.

Or give it to people who are less fortunate than yourself, someone homeless would need that 20 dollars or something. You could do many things really, its up to you. Only you know what you need to do, no of us really have the final say so.