Except as provided in 19-20-305 and 19-20-306, the retirement allowances or any other benefits accrued or accruing to any person under the provisions of the retirement system and the accumulated contributions and cash and securities in the various funds of the retirement system are:
(1) exempted from any county or municipal tax except for a refund paid under 19-20-603 of a member's contributions picked up by an employer after June 30, 1985, as provided in 19-20-602;
(2) not subject to execution, garnishment, attachment by trustee process or otherwise, in law or equity, or any other process; and
(3) unassignable except as specifically provided in this chapter.