If an item is posted a certain price that is what you pay no matter what the scanner or managers say. They can change the tag but still have to honor the posted price that you saw.
My hubby and I were shopping at Home Depot for a tree. Found a great one and the sgin on the tree read $14.99. Check out person said wrong, that is a $45.00 tree. Called the manager and he agreed that it was $45 but because the sign was the lesser amount that is what we paid. By the way, the manager sent someone out to check all the prices on every tree that very minute.