ApexPC:And WGT calculates scoring average to 3 decimal places
Ehm - excuse me, they aren't calculated in decimals but in binary ;)
Other than that, any proof to that limitation? I'd take it as granted that they use common computer number precision for their calculations, internally. Excel, for instance, uses 8 Bytes per number which results in more than 15 decimal digits resolution.
And, nitpickingly, 67.001 isn't achievable by a TP. His average of 25 scores (in saturation) may only differ by 1/25 which is 0.04. Thus possible averages are 67.04, 67.00, ...
Only Legends and up have to deal with the hidden third digit since their smallest variation in saturation is 1/500 = 0.002 or 1/200 = 0.005. Thus, their thresholds are 60.000 and 59.000 for L=>TL and TL=>C transitions respectively.