The tap tempo circuit averages the taps over the last few taps (a variable number, but more than 2). Since the purpose of tap tempo is to allow you to set the tempo to the beat, this is (we think) the best way to do it. If one was to average over a longer period, the tempo would drift around and not relate to the beat.
If you want to set the tempo to an exact value, you can do this with the encoder whenever the tempo is displayed.
Audio tapping is not something that we are considering at the moment.