first thing, always use code to format your SQL code and please also remember to mention the error you receive.

if you are using this code in post-insert or post-update of your block, it is ok and don't issue: commit.

you have used commit two times, only use after end if.

you do not have to use table name in where clause before field name when you are updating/selecting/deleting to one table.

it is good practice to use count() to check records, as it is more controlable.

MERGE INTO bonuses D
   USING (SELECT employee_id, salary, department_id FROM employees
   WHERE department_id = 80) S
   ON (D.employee_id = S.employee_id)
   WHEN MATCHED THEN UPDATE SET D.bonus = D.bonus + S.salary*.01
   WHEN NOT MATCHED THEN INSERT (D.employee_id, D.bonus)
   VALUES (S.employee_id, S.salary*0.1);