It's really f**king hard to find anything to confirm how teams are split, I remember reading on the old NRL site regards it going to percentages, but as far as reference material goes, the new site sucks balls.
What i did find was the following on the NSWRL site regards their competitions, which if the NRL uses the same criteria, then that would suggest I am wrong.above ( you'd think they would )
10.5. If teams are on equal points at the end of the competition regular season, “for and against” points will determine semi-final placings for all positions. If equal, most points for will determine placings followed by least points against. If the same, then individualresults of both teams playing each other will be taken into account (no play offs
https://www.nswrl.com.au/siteassets...s---handbook-rules-and-by-laws-final-copy.pdf