I don't do the "megalo" type places. People who love 'em ... great. For them. And if they believe validation of receipts upon exit, despite having just come from the cashier line, is the right thing to do, that's okay. Again, for them. I'll go elsewhere.
Myself, I do the smaller groceries. Of course, compared to small farmer's markets, they're still considered "supermarkets" (aka, "supermarchés"). While manual check-out stalls are provided, it's still the rare occurrence where it's ccard-only or where a staffed lane isn't also available. I do the quickie DIY checkout stall, with cash. Almost never do I find there's no cashier lane also running, though often there's only one. Works fine, though takes a little longer. Works for me.
The beauty of such DIY checkout stalls, too, is: they'll take $100s and $50s. Have yet to find any that didn't.
On the few occasions where I've been in a grocery where they won't take cash ... I walk, and they're left with the couple of bags' worth of grocery items they need to re-shelve. If disallowing "legal tender" is what they want to do, basing their business model of such choices, they're welcome to it.