I can't even remember the last time I got the wrong change back, either too much or not enough. I guess between using mostly debit card, and not often counting when using cash... actually I mostly just use cash at the honor system veggie stand. No change there at all.
Finding money on the ground is a pretty rare too, and I guess its either obvious where it came from, or it's mine.
Last thing I found on the ground was a cell phone, on a trail in french creek. Redialed the last number, asked them who's phone it was (their dad's) and to have them call my cell. Made arrangements to meet the next day since I was going to be in his area and gave it back. Dude tried to give me $5. As if that's all my karma is worth.