Commencing October 1, 2005, each person whose employer participated in the Employees’ Retirement System pursuant to Sections 36-27-7 and 36-27-7.1, whose effective date of retirement for purposes of receiving benefits from the Employees’ Retirement System is prior to October 1, 2004, and who is receiving a monthly allowance or is eligible to receive a monthly allowance from the Employees’ Retirement System, shall receive a cost-of-living increase as described in Section 36-27-190. Beneficiaries of deceased members or deceased retirees of employers participating in the Employees’ Retirement System pursuant to Sections 36-27-7 and 36-27-7.1, shall receive a cost-of-living increase of four percent in their gross monthly benefit, but not less than fifteen dollars ($15) per month.