A8 Series Ties
A8.1 If there is a series score tie between two or more boats, each boat’s race scores shall be listed in order of best to worst, and at the first point(s) where there is a difference the tie shall be broken in favor of the boat(s) with the best score(s). No excluded scores shall be used.
A8.2 If a tie still remains between two or more boats, they shall be ranked in order of their scores in the last race. Any remaining ties shall be broken by using the tied boats’ scores in the next-to-last race and so on until all ties are broken. These scores shall be used even if some of them are excluded scores.
The above is reproduced from the US Sailing web site.