If y is omitted, x is rounded to zero decimal places.
If y is negative, x is rounded to the left of the decimal point.
The following example uses ROUND() to display the result of rounding 5.75 to zero, 1, and -1 decimal places, respectively:
SQL>
SQL> SELECT ROUND(5.75), ROUND(5.75, 1), ROUND(5.75, -1) FROM dual;
ROUND(5.75) ROUND(5.75,1) ROUND(5.75,-1)
----------- ------------- --------------
6 5.8 10
SQL>