The Objective and Subjective Nature of Morality

Author Joseph Myers asks:

"Morality is relative. It is seen as a circumstantial stewardship of good instead of a constant set of settled rules...good or bad...thoughts?"

I definitely believe in moral absolutes (e.g. adultery is always wrong) but there's a particular scenario that I've been thinking about that makes me think sometimes there might be relatives. I would love to hear responses to this:

If I find a Salmon P. Chase $10,000 bill (which has not been printed since 1946) then I think it's morally incumbent on me to make some attempt to find the rare bill's owner.

But if I see a penny on the ground, I think nothing of simply picking it up and walking away.