Section 50. The auditors of a town shall examine the books and accounts of all its officers and committees intrusted with the receipt, custody or expenditure of money, and all original bills and vouchers on which money has been or may be paid from its treasury. They shall have free access to such books, accounts, bills and vouchers as often as once a month for the purpose of examination, and shall examine the same at least once in each year, and annually report in writing the result of their examinations. They shall, at least once in each year, verify the cash balance of each of such officers and committees 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.