Olympic and similar competitions are timed to the nearest 1,000th of a second, but any result within the same 100th is considered a tie as that last bit is just entirely arbitrary, in part because pool dimensions themselves are not accurate to this degree. (The FINA standards mentioned in my earlier comment addresses dimensions accuracy standards.) The Olympics did break ties at the 1/1,000s standard in 1972, but has since judged any result within 1/100th as a tie:

<https://olympstats.com/2014/02/12/timing-accuracy-at-the-oly...>