There are several US states where, by law, retailers are not allowed to give preferential treatment to credit card paying customers over cash paying ones. Which means, in those states, retailers will be required to always round transactions to the cash paying customer's benefit, where in other states the retailer is allowed to round to the nearest 5 cents. This is going to cost large retailers millions.

Interestingly many of them had already put the work into updating the cash register software to allow for this due to the penny shortages during covid.

Let those large retailers put pressure on their suppliers. Prices haven't exactly been stable recently. I really don't think it matters, but if it did (as you claim) then surely some downward pressure is a good thing.

It doesn't cost anyone anything. They can just raise prices 3 cents or whatever.