Retailer here: Most of these costs are fairly fixed. We have to have a safe, bags, armored transport, staff training on counterfeit detection, etc. whether the percentage of our sales in cash is 8% or 80%. The few costs that are variable are still far, far less than the processing fees.

It's also worth noting there are also huge fixed costs for credit card transactions. We're currently upgrading our pinpads and it's been an absolute nightmare to get the right parts in just for physically connecting the damn things to our counters, we lost almost a whole day of backend POS access for our vendor to push a required update, and I'm looking at more fees to be able to support other types of cards which require POS certification.

We strongly prefer our customers use cash.