Hand back the extra change. Integrity mostly gets tested in amounts too small to brag about.

Character is rarely examined in dramatic situations. It gets decided in moments so small that nobody would ever know either way, which is exactly what makes them the real test. There is no audience, no story afterwards, and no reward beyond knowing which way you went. Those are the choices that quietly set what you will do when something larger is at stake.

When a small chance to keep something appears, notice it as a decision rather than an accident. Hand it back without making it a moment. The point is not the money, it is which habit you are feeding.