An extract from the Boeing 737 (NG) FCTM, page 4.10.
Fuel for Enroute Climb
The additional fuel required for a 4,000 foot enroute climb varies from 300 to 500 lbs (135 to 225 kgs) depending on the airplane gross weight, initial altitude, air temperature, and climb speed. The fuel increment is largest for high gross weights and low initial altitudes. Additional fuel burn is offset by fuel savings in the descent. It is usually beneficial to climb to a higher altitude if recommended by the FMC or the flight plan, provided the wind information used is reliable.
Note: The fuel saved at higher altitude does not normally justify a step climb unless the cruise time of the higher altitude is approximately 20 minutes or longer.
No try telling the last part to captains who obsess with the fuel league and insist on going up to FL410 a few minutes before descent...