Are you saying that stores in the 2000s were throwing away 20% more of their total revenue than they are today? That sounds crazy, especially given that the prices - again - seem pretty much the same or higher if you correct for inflation.
But more to the point, there's plenty of grocery stores that ask 20% more than their competitors and are doing just fine; in fact, constant price changes and promotions make it impossible for consumers to really compare if Safeway is cheaper than Whole Foods, so people usually go to the place that's physically closer, has better selection, or better vibes. I can't even know if a 12-pack of Coca-Cola is going to be $6.99 or $9.99 today.
Coca cola is a bad example as it does not require refrigeration during transport and does not spoil fast (at all?).
Choose your own number, but it has to be large enough that supermarkets decided the CapEx was worth it, and also large enough that once one did it, the rest followed suit.
It's not even significant cost. The main cost is still the hardware, not electronics driving it, and especially not a tiny module that talks with electronics to send/receive commands/metrics