Our Micros systems are set up to use the following procedure... Not sure about others
We first select the void button, then Non Revenu service charge button, then enter the amount we wish to refund and get a negative check amt. then authorize the credit card you want to apply the refund to on this check and settle it for that amount.
Note: the card auth will not show a negative amt and when you enter the amt to settle card for you will enter in a positive as well..... seems a little wrong the first time I did it but it works and process a credit back to the card. Just be sure void is on before you hit the non revenue button