I am in the process of interviewing for faculty positions and trying to keep my CV up to date as I go. Should I include research (or teaching) presentations given during on-campus interviews as invited talks? Or are they considered just a part of the interview process and better left off the CV?
I would say no. Leave them off the CV.
Apart from the fact that you more-or-less invited them to invite you by applying for the position, thus they are not really invited talks, it's probably not a good idea to advertise all of the places you've unsuccessfully applied to or declined.