If accuracy is important, consider using a current drive circuit (i.e. constant current source) to power each LED rather than the basic method of placing a resistor in series with a voltage source. Then you won't need to worry about the knowing the exact forward voltage of the LED. Incidently the VI curves for LEDs are temperature dependent.

If a constant current source is too complicated, you can approximate the forward characteristic of the diode using a pieceweise linear model, ie. a forward voltage plus a resistance. See the example [here][1]. From this it should be straighforward to get the current at 100mA.


  [1]: http://en.wikipedia.org/wiki/Diode_modelling#Diode-resistor_circuit_example