ARAM Medals

I've always enjoyed playing ARAM gams since they are casual and fun. Its a place where you can do very strange builds like full AP zac and just have fun.I've been looking at my profile where it shows takedowns, towers, cs, dominion points, and all that. You are able to get the bronze through diamond medals on Classic, Dominion, and ARAM. I am still very very confused on how to ARAM towers destroyed works. I just won a game as Sona on aram (5/0/52) and got 2 towers destroyed. I figured I would have gotten 5. Do I need to get an assist on the tower or get the actual last hit?