Referencing NH Code of Administrative Rules, MUR 300
Trustee Meeting Minutes: forever
Town Reports: forever
Personnel files: until 7 years after employee leaves
Payroll files: until audited plus 1 year
Checks and bills: for 6 years
Patron registration cards: until 1 year after the expiration date
For regulations regarding other records see the above mentioned code which can be found at http://gencourt.state.nh.us/rules/mur.html.
Record retention is found particularly in part 303.