These days, most people won't bother to pick up a coin on the floor unless it's at least a quarter.
If you were at the grocery store and found a quarter, you'd probably smile at your good fortune, pick it up, and put it in your pocket. Would you even consider taking it to Customer Service to report it as lost? Try it some time, and record the bemused look on the associate's face. Your honesty will probably make the rounds of the breakroom for the rest of the day.
Why do we consider a quarter so insignificant? We cannot know the true value of that quarter to the person that lost it, but we judge based solely on our own situation that the quarter is virtually meaningless -- although not quite meaningless, as we willingly bent over to pick it up.
If we found a wallet, whether it had ID included or not, most of us would probably take it to Customer Service, yes? Perhaps the wallet only included a quarter, but we'd still turn in the wallet. But what if we found ten wallet-less dollars. What would we do then? Would we turn in the money? Is there a monetary amount where pocketing the money without seeking the person that lost it is wrong?
Does the answer change depending on context? If we found ten dollars at the playground in the local park rather than at the grocery store checkout, would we be more inclined simply to pocket the money?
Should ethics be situational? Contextual?
"Life is essentially a question of values." -- Meir Kahane