I know that Whole Foods employs these kinds of tactics all the time. As an anecdote, a few weeks ago I went there to buy some sunflowers for my girlfriend and was happy to see them marked at "2 for $10." When I went to pay, the cashier said, "Ah, so the price of these went up!" I asked her what she meant, thinking it odd since they were on supposedly on sale. She told me they were $4 the previous week, must've been they were getting popular.

So what they did was mask the price hike with the veneer of a promotion, which is equal parts clever and cruel. Here are a couple of photos of other pricing tricks they've played:

1) http://cl.ly/image/102k133G2L3B 2) http://cl.ly/image/3a1q002M1G05