Sec. 10.04. INTEREST ON INDIVIDUAL ACCOUNTS. The fund shall credit interest on December 31 of each year to the account of each firefighter, and of each former firefighter, who has not retired in an amount equal to five percent of the accumulated contributions, including previously credited interest, on deposit on January 1 of that year. The fund may not pay interest on a firefighter's or former firefighter's contributions for part of a year or for any period that is more than five calendar years after the date of termination of employment.