Interest shall be credited to the account of each member once each year as of June thirtieth, on the basis of the balance in the account of each member as of the previous June thirtieth. Upon the death, retirement, or termination of a member, interest shall be figured to the end of the month immediately preceding the date of refund or retirement, interest being based on the balance in such member's account as of the June thirtieth immediately preceding the date of refund or retirement.