N.H. Rev. Stat. Ann. § 33:16

All bonds and notes, and the interest thereon, heretofore or hereafter issued by municipal corporations and counties under the provisions of this chapter or of any general or special act, heretofore or hereafter enacted, shall be exempt from taxation in the state of New Hampshire. For the purpose of this section the amount of the discount on any notes which are sold at discount shall be deemed to be interest paid in advance.