At least once a year the town board must meet as the "board of audit" to audit and settle all charges against the town. Minn. Stat. 366.20. The board of audit can be held anytime following the close of the fiscal year (December 31) and up to a week prior to the annual meeting. 

The duties of the board of audit are specified clearly in the state statutes. Minn. Stat. 366.21.

In preparation for the board of audit activities, the treasurer is required to prepare and file with the clerk at least 5 days before the annual meeting a written statement of money received from any source and all money paid out as treasurer. Minn. Stat. 367.16.  The treasurer is also required to provide the board of audit the book of accounts along with the treasurer's vouchers.

The clerk is required to furnish a statement from the county treasurer of money paid to the town treasurer, all information about the fiscal affairs of the town in the clerk's possession, and all accounts, claims, and demands against the town filed with the clerk. Minn. Stat 367.11

Much of the work of the board of audit is performed at the town board's regular monthly meeting when it reviews and approves claims for payment. It therefore is not necessary for the board to re-examine each claim in detail at the annual board of audit. However, the town board must formally sit as the board of audit to review the town's account for the year and develop the following years budget.

If the board chooses, or is required, to have a CPA perform an audit of the town's financial affairs, it must still perform the duties of the annual board of audit. Of course, the fact that the audit is already completed will make it much easier for the board to complete it's duties.