ROUND returns a date rounded to the unit specified by the date format.
DATE
ROUND(date [, fmt ])
date is an expression that identifies a date and time.
fmt is a text literal with a date format, as described in the Oracle Database SQL Language Reference.
ROUND(SYSDATE, 'YEAR') returns the value 01-JAN-07 for any day in the last half of 2006.
ROUND(TO_DATE('13-OCT-06'), 'MONTH') returns the value 01-OCT-06.