For a tie, it would be based on the round you played against that player and not on previous rounds. I included information about ties below from our FAQ section here: http://www.wgt.com/help.aspx
In the event of a tie, the better scoring entrant between or among the tied entrants will be the entrant with the lowest combined score for the final nine (9) holes of the Game. If any ties remain, the better scoring entrant between or among the remaining tied entrants will be the entrant with the lowest combined score for the final six (6) holes for such Game. If any ties remain, the better scoring entrant between or among the remaining tied entrants will be the entrant with the lowest combined score for the final three (3) holes for such Game. If any ties remain, the better scoring entrant between or among the remaining tied entrants will be the entrant with the lowest score for the 18th hole (9th for nine hole games) in such Game, and any remaining ties will be determined by identifying the lowest scoring entrant for each individual game hole, in sequence from 17th (8th for nine hole games) through to 1st, as is necessary to determine a winner, and if any ties remain at that point, the earlier-submitted entry between or among the tied entries will be deemed the better scoring entry.
Best,
WGTShamWow