Numeric Math Functions Oracle PLSQL

SQL>
SQL> SELECT TO_CHAR(ROUND(TO_DATE('25-MAY-2005 19:45:26','DD-MON-YYYY HH24:MI:SS
'), 'HH24'), 'DD-MON-YYYY HH24:MI:SS') FROM dual;
TO_CHAR(ROUND(TO_DAT
--------------------
25-MAY-2005 20:00:00
SQL>
SQL>
SQL>