I think there may be a labelling law that covers that. I believe that they label on any package has to be an accurate reflection of the package's price. Things like meat that are prepackaged but sold by weight have to be individually labelled/priced on the shelf. Each jurisdiction will have its own rules but they all came from a time in the 1950s when evil supermarkets were attempting to hide higher prices on groceries knowing that few people would check their receipts against the shelf prices.

https://www.nist.gov/system/files/documents/2017/04/28/US-Pr...

Arizona:

F. Except as otherwise provided in this chapter or by rules adopted pursuant to this chapter, any package kept for the purpose of sale or offered or exposed for sale shall bear on the outside of the package a definite, plain and conspicuous declaration of: 4. The price, except as provided in subsections K and L.

DC:

(6) DISPLAY AND ADVERTISING OF CONSUMER COMMODITY UNIT PRICES.--A seller shall conspicuously and clearly display the price per package or unit and the unit price in close proximity to the display of the commodity