AFAIK, Wal-Mart is the only retail store that negotiates directly with Visa and MasterCard, and that only really happened after it sued both card networks a decade ago over being forced to accept cards with higher fees if it wanted to accept debit in its stores. They're still not happy with what they're paying; they urged a rejection of the settlement offer in the latest class action suits over processing fees because it still left Visa/MC's ability to raise those fees when they want intact.

So it's likely even large chains like McDonalds still pay the 1-2% interchange rates everyone else pays, just with a lower markup than average. They do pre-negotiate rates on behalf of their franchisees, which own the merchant accounts for their individual stores.

Even they don't get lower rates than interchange, because issuing banks get that no matter what. But they can get a very low margin above that.

almost certainly cheaper, but i doubt they ever make it to pennies per transaction. the best rates I have heard about are 1.6% + 20-30c