Well, Old Smokey's trick to " soft reboot " the VNAV function of the FMC does seem to work in getting the calculated figure to reconcile with the totalizer. However, in many many flights where the flight was exactly conducted as per computer flight plan ( as far as TOWs, routes and flight levels are concerned ), the calculated figures are almost equal to the computed flight plan figures at the various check waypoints. On the other hand the totalizer figures fluctuated from plus to minus several hundreds of kgs! By " soft rebooting " the VNAV function, the calculated figure almost immediately equals the totalizer and as time goes on, the two values start to drift apart again.
I still think that the totalizer suffers from inaccuracies in the FQIS; B777 drivers should heed woody spooney's warning about the totalizer misleading the unlucky ones who get slow fuel leaks.