I don't know what the rules are for being able to declare sale prices in America, but in the UK we have some regulations.
Regulations that are bent to the point of stupidity.
One is, to claim you have reduced your price, you must have been selling it in at least one store at that price for 28days.
So, the likes of Wallmart can put their price up in one single store (probably an out of the way one that the locals have to buy it at that price thru lack of an alternative shop) then claim a discount everywhere when they drop it back down.
Reminds me of the time I was laid off from a job, then they wanted to hire me as an outside consultant. The Director of the facility was concerned I was going to want $80/hr. I then stated, good, I am only going to charge $79.99/hr. My former boss was laughing her butt off.