Porcelain tile, Seal or no seal?

I recently placed porcelain tile in my kitchen and dining room. I am having conflicting answers to my question as to can I seal it or not. The finish on the porcelain is not lustress, but if there is a seal than I can roll over the tile and grout, without hurting the tile, that will add some lustre to the tile and do the job, them I am all for it. My questions are, is there a seal that I can roll over both and be fine, or do I need to just seal the grout? Thanks for your help.

John