N.H. Rev. Stat. Ann. § 78-E:7

Notwithstanding the provisions of this chapter, if a New Hampshire remote seller is determined to be obligated to collect and remit a sales or use tax on behalf of a foreign taxing jurisdiction or foreign taxing authority, then that New Hampshire remote seller shall be entitled to recover or deduct from any taxes collected on behalf of such foreign taxing jurisdiction or foreign taxing authority any reasonable costs, including any initial set up and ongoing maintenance costs, incurred in the collection and remission of sales and use taxes to that jurisdiction or authority.