the AI of towers is actually pretty dumb.
Case in Point: I've learned that if I play Heimer, I can freely tower dive with my team basically for free 100% of the time. The Tower AI is for SOME reason coded so it will automatically target Heimers normal or Ult turrets over minions first and foremost. That part is fine for the most part, I get why, but the problem is, the AI of the tower is also coded to never CHANGE targets from that turret until it is dead.
Multiple times I will walk up to a tower with a friend, drop my ult turret, Tower targets it. Walk in and kill whoever is under that tower and the tower will never change targets because it is coded to go ham on Heimer turrets 100% (I'm actually not certain it won't target the turret over a champion even if a champ is being already targeted but I've yet to bother testing it).
I was showing this to my friend the other day and it just blew his mind, because from then on we could tower dive for free as long as I had ult turret up (just because it has a bit more health is all). The tower AI pretty badly needs to be fixed on a lot of levels because it makes some silly situations and interactions otherwise.