Trillinon is right, it doesn't really declare what happens on ties. At the very least it could make a comment like "See individual uses for what happens when one wins, loses, or ties during an opposed test.
But then again, you could just take the term "tie" at face value. There are a couple of instances where it specifically says who wins and who loses on a tie, but otherwise it could just be that nobody won. For example, when I'm running Matrix related tests (specifically Attack/Sleaze actions), on a tie, nothing happens. The enemy didn't win, so they don't get the advantage, and the character didn't win either so they don't get what they were trying to do. There are a lot of cases where ties can totally be a third option between one side winning and the other.