The books, accounts, and vouchers of the county treasurer, and all monies, warrants or orders remaining in the treasury, shall at all times be subject to the inspection and examination of the board of county commissioners, and at the regular meetings of the board in January and July of each year, and at such other times as they may direct, he shall settle with them his accounts as treasurer, and for that purpose he shall exhibit to them all his books, accounts and money, and all the vouchers relating to the same, to be audited and allowed, which vouchers shall be retained by them for evidence of his settlement; and if found correct the accounts shall be so certified; if not he shall be liable on his bond.