Sometimes card is quicker. I know at my Tesco I'm quicker getting through using a card, but hate it when I'm stuck behind someone who goes through and counts their coins, or the cashier has to root around for change.

With the card it's just swipe and pin. Done.

Also the minimum is against Visa's merchant agreement. You can report them to visa to get that changed. I was at a pub once that said £10 minimum, but just before I was going to argue he said he would charge it up for £10 and give me the change. Fair enough I suppose.