It's actually not that uncommon for people to turn in lost cash if it's more than like $5. Happened fairly frequently when I worked retail/hospitality.

Most people are decent and honest and know how they would feel if they lost a larger sum of money. Although I get keeping it if you can't reasonably ascertain what location the person who lost it was visiting. No one is going to think to check with the police for $30 they randomly dropped in the street. ****