Except as provided in subsection (b) of this section, regular interest is payable on member contributions until retirement or withdrawal of accumulated contributions at the rate of: 4% a year, compounded annually, for a member who has transferred from the Employees’ Retirement System; or 5% a year, compounded annually, for each other member. No further interest shall be paid on member contributions after membership ends if the former member is not eligible to receive a vested allowance under Title 29, Subtitle 3 of this article.