There are different versions of TTL and I don't know for sure which one the F5 supports. While traditional TTL furnished a trigger and a quench signal, more modern systems run a clock/data protocol over the same pins to communicate settings and sensor data between flash and camera. Since digital cameras can't use traditional TTL, they are tied to that more advanced TTL system.
In theory analog cameras could implement the same fancy protocol between flash and camera, and in Canon land later analog models like my EOS 3 fully support modern E-TTL flashes and accessories. From superficially looking over Nikon data sheets there appears a distinction between the F5 with TTL and e.g. the D60 with i-TTL.
I know the Nikon F6 supports D-TTL. Unfortunately, I can't afford an F6 quite yet.