Happened to me yesterday. Haagendaz ice cream. $4 on the shelf, $5 at the register.
If it says $4 on the shelf and you pay $4 at the register and walk out with the goods, that's a 100% legal sale and not theft. Not even if it was a mistake on the part of some employee (and it's not the employee's fault either, by the way)
It literally is the employee's fault but they are not legally liable for it.