Ahh thanks for the correction. This seems like it's still pretty consumer unfriendly though - you still have to advertise the card price in store and then you can take a discount at the register, as opposed to advertising a cash price and then adding a card charge.
There are a lot of small businesses around me that are cash only under $10/15 dollars. Given human psychology around advertised prices (i.e. most people don't think about opportunity cost), I'm not surprised cash discounts aren't common.