The retirement system may, in the exercise of its constitutional discretion to manage the assets of the retirement system, select one or more commercial banks, depository trust companies, or other entities to serve as custodian or custodians of the system’s cash or securities pending completion of an investment transaction and may authorize such custodian to invest the cash so held in such short-term securities as the board of trustees determines, subject only to the provisions of § 840.301 of this subtitle.