There is a 5% tax on interest and divindends. An individual whose interest and dividends total 2400 or married totaling 4800 must file NH Form DP-10. Your prtfolio gains and losses are also reported on the form but there is no tax consequence.
This tax also applies to and LLC, partnership or sole proprietors whose interst and dividends total 2400 or more.
The tax return is due April 15th on every year. It should be noted that there is a 1200 exemption for individuals over the age of 65.
www.NH.gov is has excellent source for questions regarding this tax as there are other items that must be reported such as distributions from an S-Corp.
By the way, yes I am a CPA.