N.H. Rev. Stat. Ann. § 28:24

All county bonds and notes, except tax anticipation notes maturing in less than one year, shall be sold at public sealed bidding to the highest bidder; provided, however, that the county commissioners may reject any and all bids and may negotiate for said sale upon terms which they deem most advantageous to the county. Any bond sold under the provisions of this chapter shall not be sold for less than par.