Earlier quoted context omitted.
obviously they pass the cost on to the customer, but not directly. they can't charge one price for cash and a different price for card.
Which means they have to pass the cost on to both kinds of customer.
From a discussion I had with a merchant, that rate is quite high, especially for small change. The value he gave for small change was 7%. That's a lot more expensive than the worst credit card charges, except for really small amounts.