Why are batting averages in baseball and softball are expressed as a decimal to the thousandths place?

That is done to ensure that a winner can be crowned for the batting title. Someone may hit .359, someone else may hit .357. If the decimal point is not carried out to the thousandth, there would be a tie for the batting title. And if there is a tie for the batting title with the average rounded at thousandths, the average will be rounded at ten thousandths to see if that would determine a winner.