Are gas stations breaking a law or something?

Ok it seems to be an ever rapidly growing trend that I go into a gas station to purchase something small, a soda or pack of gum or something and when i get ready to check out i swipe my debit card (as I rarely ever carry cash) and the store clerk tells me there is a $5 minimum to use my card so I end up having to buy candy or a magazine or something I didn't need in order to get above $5. I understand the store has a surcharge they have to pay every time someone uses a card but that's the cost of doing business and I shouldn't have to pay that. In addition they have started doing it with fuel purchases also. Like today for example cash price is $2.18 per gallon and credit/debit price is $2.28 per gallon. So I have a 20 gallon tank so I payed an extra $2 to fill it vs someone who uses cash for the exact same product. Im sure everyone is saying just go to another station but literally all of them I go to has this policy. It is very annoying not to mention it almost has to be illegal. Anyone else had this experience or know of the legality of this issue?