Superstore, discount, cheap, etc are VERY general keywords. What you want is highly targeted traffic - or people who know exactly what they want and land on your site expecting to find it.
When I go to the mall or to WalMart, I might browse and buy this and that. But when I shop online I search for what I want and purchase it. Today for example, I typed in "lounge chair" and searched to find what style I wanted and what the prices were. My daughter was searching for a moon chair later when I walked through the room.
Even those were pretty general searches, and more to 'browse' and get an idea of price & availability. More specific terms (that would show a person is closer to buying) might be: lounge chair cushion, lounge chair cover, cedar lounge chair, InStep lounge chair, Adirondack lounge chair.
Thats what you want when it comes to keyword advertising - specific keyword phrases that point to internal pages that offer specific products. That kind of traffic has a much higher conversion rate - where general keyword searches have a 0-low conversion rate.