This has happened to me as well and I went directly into the bank with the ATM card after I hit "Cancel" on the screens. I too was raised to do the right thing, I'd never, ever even think of stealing someone else's money.

I've also come upon a car with its car keys sitting in the door's key hole. I took them into the library where the car was parked and they found the owner inside.

What goes around comes around. Even if "no one would know", God does...and so would I.