According to the Yahoo rules, here's the tie break system:

Overall winning percentage.
Fantasy points scored.
Fantasy points scored in Week 17.
Fantasy points scored in Week 16.
Fantasy points scored in Week 15.
Fantasy points scored in Week 14.
Fantasy points scored in Week 13.
Fantasy points scored in Week 12.
Fantasy points scored in Week 11.
Fantasy points scored in Week 10.
Fantasy points scored in Week 9.
Fantasy points scored in Week 8.
Fantasy points scored in Week 7.
Fantasy points scored in Week 6.
Fantasy points scored in Week 5.
Fantasy points scored in Week 4.
Fantasy points scored in Week 3.
Fantasy points scored in Week 2.
Fantasy points scored in Week 1.
Random "coin flip"

It actually makes more sense to have it head-to-head first, but there's no way to change it on the system (that I know of, anyway).