Yes it can. You are going to a building (or shop) owned by Tesco, and it's just like going to a house owned by your mate Steve. You could go to Steve's, or you could go to Tesco's.No. It can never be Tesco's when saying: "I'm going to..." "Guess who I just met in..." "I've just been to..." ~ it's always Tesco. You could, however, say that Tesco's fish is rather nice.