This is a good bug report, thank you u/blurrel!
When your game client sends aim vectors up to the game server, it quantizes the values (rounds down to a sub-fraction).
We did this to save bandwidth, for both your local network, as well as our game hosts.
But we can't just network the quantized values, we also make you play with them locally. We do so because we don't want you to have accuracy greater than what the game server would receive -- that would cause Hit Registration desyncs.
I'll make sure we increase the rounding precision in a future patch, thank you.