Your tiebreak score is equal to the cumulative scores of the people you have defeated in a tournament round.
For example, if you beat A once, and their score is 2 and you beat B twice and their score is 1.5 your tiebreak will equal 5.
If their is a tie in a round the tiebreak score breaks, if there is a tie with tiebreak both people advance.
I have looked around the site and I haven't been able to determine how the tie breaks work. If some one could explain I would appreciate it.