The board shall, from time to time, establish such rules and regulations for meetings of the board and for the administration of the fund, and the various accounts thereof, as may be deemed necessary. The board may, by January 31 of each year, determine the rate of regular interest to be allowed member contribution accounts for the current calendar year, such rate of regular interest not to be less than four per cent nor more than five and one-half per cent per year. It shall keep such data as shall be necessary for actuarial valuation purposes. The actuary of the board shall (i) periodically make an actuarial investigation into the mortality and service experience of the contributors to and beneficiaries of the fund, (ii) adopt for the retirement system one or more mortality tables, and (iii) certify to the board annually the amount of appropriation to be made by the county to the fund to build up and maintain adequate reserves for the payment of the county's share of the retirement allowances.