Oicur12,
We would add additional taxi fuel with a 10 minute minimum plus at a fixed amount for each expected minute longer than that. The 10% can be used following that but the idea is to have it for flight rather than on the ground.
We generally tanker away from base to maximum landing weight, so its quite common to see our B777's arrive over LHR with 30,000 fuel remaining! Crews are never questioned about adding additional fuel.
Dreamland... what were you trying to explain?
Mutt