Im assuming by hardware store, your rocks arent from an aquarium store and havent been sold specifically for use in aquariums. So, I would test the rocks to see if they will cause you any issues first. A few drops of vinegar on them and if the vinegar fizzes, the rock contains calcium which could cause problems with your pH.
If you are happy with the rock types though, i would run very hot water over them to kill off any bacteria before putting them in your aquarium. Boiling or baking is often recommended, but this runs the risk of explosions. If you do choose to use boiling water, pour it over the rocks rather than boiling them in a pot to reduce the risk.