The only scenario in which a single vote can determine the outcome is one where exactly one vote separates two governing coalitions. Since that has never happened, and in fact has never come remotely close to happening, it is almost always pointless to vote.
This is not true, see https://people.howstuffworks.com/can-single-vote-change-election-outcome.htm and https://www.npr.org/2017/12/19/572082933/a-single-vote-has-flipped-control-of-virginias-house-of-delegates
From what I understand they cut off the extra digit(s) at birth, so you wouldn’t know unless you asked them.