Section 53. Town auditors shall at least once every year, and so much oftener as they deem necessary, audit the accounts of the trustees of any property the principal or income of which, in whole or in part, was bequeathed or given in trust for public uses for the benefit of the town or any part thereof, or for the benefit of the inhabitants of the town or of any part thereof, and examine and estimate the funds, securities and evidences of property held by such trustees. Said trustees shall give said auditors free access to their accounts, funds, securities and evidences of property; and any such trustee refusing to exhibit the same shall be punished by a fine of not less than fifty nor more than two hundred dollars. Town auditors shall include in their annual reports a report of such auditing and investigation; and if they discover any fraud or irregularity they shall immediately report the same to the mayor and city treasurer or to the selectmen and town treasurer. They shall, at least once in each year, verify the cash balance of such trustees by actual count of the cash and by reconciliation of bank balances, and shall insert in their annual report their certificate under oath of the facts so found; provided, however, that they need not so verify the cash balance by actual count of the cash if the trustee is a bank, banking association or trust company.