Scoring is done via the ten-point must system meaning that the winner of a round must get ten points. The only instance in which there can be a 9-9 round is if a fighter wins a round but is docked a point for committing a foul of some sort.
As for a knockdown always meaning the knocked down fighter always loses the round via a 10-8 score, that's not automatically the case. There've been many cases when the dropped fighter dominates the rest of the round & the judges have only scored it a 10-9 round. In fact, it just happened in the Joseph Parker - Derrick Chisora fight in round one.