I think this is a common thing in small groceries that simply don't have their shit together. I know a few small or independent grocers in NYC with the same exact issue. I complained a million times, it never got better.

I don't think it's super intentional, I think it's more that the register updates the prices all at once and they don't have their shit together enough to change all the prices in a single night.

Doesn't make it right or anything, just my thoughts. I try not to assign malice in instances where incompetence could be the cause.