Have you ever seen those signs at cash registers that say consumers must spend a minimum amount -- often $10 before they can use their credit card? That is specifically against the rules. I ignore those signs and charge whatever I want and you can too.
Download this wallet card PDF. It has the merchant agreements in plain English that makes the minimum charge against the rules. Blogger Andy Jones put it together and suggests consumers download the card, and whip it out the next time they see one of those minimum purchase signs at a cash register.