Under the previous Survivor system of a final 2 with an odd number of jury members, a tie was impossible. With the change to a final 3, there had to be a tiebreaker as there is too much "sole Survivor" hype to allow a final tie.In order for a tie to exist with a final 3 and seven-person jury, the votes have to be split 3-3-1. I would have the person who voted for the third-place finisher re-vote between the top two and break the tie.
The situation is more difficult with a final 3 and nine-person jury. While a 4-4-1 tie is resolved as above, how do you handle a 3-3-3 tie? That may be why they changed the format to a seven-person jury with a final 3.