What does "Round-Up" mean?

“Round-up” is a term used to refer to your spare change after making a credit/debit card transaction.

For example, if you bought lunch for $7.61 on a credit/debit card that is registered for round-up by Altruist Give, the corresponding change it would take to round-up to the nearest dollar, $0.39, would be donated to the non-profit organization of your choice.