Each council of government established under authority of this article exists for nonprofit and public purposes and is a public agency, and the carrying out of the purpose of each council of government is exclusively for public benefit and its property is public property, and no council of government is required to pay any state or local ad valorem tax, income tax, or other taxes from which public agencies are exempt. Councils of government may participate in the State Retirement System and utilize the services of the State Purchasing Department of the Division of General Services.