a question about crit chance runes

I heard ages ago they don't round and it's the value you see on the rune

No, decimals don't round.

You get .9%, even if the in-game numbers round.

This is why things like cannot kill you with the burn, because in the end it's just doing decimal damage, even if you have 1hp.

The values are rounded for display purposes in-game.

However, for the purpose of calculations they use unrounded values.

Actual math on whether or not you crit? No In game displaying of your crit chance? Yes it rounds.