Syntax:
ROUND(X), ROUND(X,D)

Rounds the argument X to D decimal places. The rounding algorithm
depends on the data type of X. D defaults to 0 if not specified. D can
be negative to cause D digits left of the decimal point of the value X
to become zero. The maximum absolute value for D is 30; any digits in
excess of 30 (or -30) are truncated. If X or D is NULL, the function
returns NULL.

URL: https://dev.mysql.com/doc/refman/8.0/en/mathematical-functions.html

