Hi
I don't think there is any variable to determine the number of sets in a tennis match, unless, as Oxa points out, the tennis_current_set shows 3 or higher.
As far as I am aware the only matches which are played to best of 5 sets are men's Grand Slam tournaments:
Australian Open
French Open
US Open
Wimbledon
Davis Cup men's used to be 5 sets but I think this is now 3, and men's Olympics final you can google to see.
All others are best of 3 sets
So you could use the market_name variable to include or exclude men's markets for the above list.