All sums collected under this chapter and any other authorized sources shall be deposited by the department into one or more accounts with one or more financial institutions opened by the department for the specific purpose of maintaining committed persons’ funds. The department shall maintain accounts for each committed person to allow committed persons use of their own funds for approved expenses and purchases during incarceration. The director may designate a percentage of all funds earned by the committed person while in custody to be deposited and held in a nonspendable account for the purpose of providing funds for that same committed person upon release from custody. The structure of these accounts shall be designed so that all funds deposited by or for a committed person shall be credited to the accounts. Accounts maintained by the department for committed persons shall not bear interest. No interest of any kind shall be paid to a committed person on any account maintained by the department for the committed person. The department shall provide quarterly accounting statements to all committed persons held in custody for over one quarter of the year. The department shall conduct annual audits on all committed persons’ accounts.