Since we are here, it would be nice to have some tie-braking criteria (what if two pizza end up with the same number of votes? Given the prize structure, avoiding doubts on the ranking system would be nice.
Since Instant-runoff voting system is used, I don't think that its possible to have a tie as the order of votes actually count so the one with highest number of first choices wins.
I totally missed where icopress said the voting system is based on the IRV.
Using this system is totally fine, yet it should be clear to everyone, and based on an “official” statement by contest organiser(s).