In addition to the 9/11 security fee you will also have to pay all Passenger Facility Charges (PFCs) and I believe that you also have to pay the per-segment flight tax. The main tax you don't pay is the 7.5% tax on the airfare since that is $0.
The PFCs for a JFK-LAS round-trip should be $8.50 per person and the Flight segment tax should be $7 per person, plus the $5 9/11 fee.