As someone who ran a gas station convenience store for six years, I can tell you that this is not a universal truth. We did require a minimum purchase amount to accept cards, but we most certainly did not raise our prices in response to credit card fees.
The majority of purchases inside the store were cash because we required a $5 dollar minimum purchase for accepting cards. Most card purchases were used for gas which was already a loss leader most months out of the year, so it made more sense to keep posted prices competitive with stations in the area in order to bring people into the store rather than charge a few more cents in order to offset the cost of cards.
I thought minimum purchase requirements were against the terms of service for most credit cards. I've bought plenty of < $1 items with my credit card. I try to use it for everything to "earn" the rewards.
