The SKU at staples doesn't matter. Whether price is full or on a discount the SKU remains the same. However, Staples clearance - all the prices end in 0. Staples will discount pretty low so be patient unless you really want/need the item. It will probably go lower.

Circuit City is similar. It's just a simple way for the associates to know which items are "clearance" and which are still at full price. Circuit City ends all of their discounted and clearance items in .96, all regular prices items in .99. I was a manager there for a long time. Most retailers are the same way. Now, just because it ends in a clearance price doesn't mean that is the absolute lowest it will go.

I worked at Target for 6 and a half years. Its true.
The only clearance prices that would be different from ending in 4 are the ones that were either repackaged, were missing pieces (i.e. 2 glasses only, originally from a package of 4, because 2 were broken) or were somehow slightly damaged, yet are re-sellable, which is kind of unlikely.
You will rarely see anything marked down below 75% unless it is one of the cases listed above, and even then its quite rare. There had been instances where I purchased product at 90% off, however, Target employees tend to have first dibs on this merchandise because they are the ones that do the markdowns and push the product to the floor.

All the clearance tags at Target have the percent printed on them at the very top in really small numbers.