Stolen from
weblamer.
Target's full prices end in 9. So the first price tag will be $14.99 or $27.99, something like that.
Then, every time Target discounts the product, the final digit of the price drops.
The lowest the last digit will drop is 4.
If you see something you want at Target and the price ends in 4, buy it. The price won't go any lower.
EDIT: I don't know how well this holds up. I've been to Target a couple of times since reading this and so far I've found no discernible pattern.