I was at the airport the other night, buying some stuff.
Total cost $41.35.
Gave the old bloke $60 (3 x $20).
I received $28.65 change, a “bonus” of $10.
Spent the next five minutes arguing with the old bloke, that he was short-changing himself $10.
Now some people might say “… serves him right, keep the extra $10.”
But the thought of the poor bloke having to make up cash from his wage stopped me doing that.