I would log it since you had taxid out with the intention to fly. Where I do not log is if i specifically taxi out to do a runup after maintenance.
Part 91 I no longer log that stuff and typically if I take my plane up just to do one lap around the pattern to check something out I usually wont log that either since it is peanuts at this stage in the game but when you are building time every (legitimate) tenth counts towards your goal.
You are not being dishonest by wanting to log the time and it is your discretion I would tell my students whether or not you choose to do so.