updated 130113
Although VASSAL can configure a die roller which no uses the Mersene Twister algorithm (see separate help file), the multiple variations of die rolls needed (1-9 Shots, bonus vs non-bonus, speed rolls, etc) would require player definition for each shot for a game requiring hundreds of die rolls. It is recommended to use one of several custom internet die rollers for VIP or one of the several generic ones.
Typically the inherent die rollers are used for server play or where players are playing known opponents who they can trust. It is possible to 'cheat' by restarting a log file to generate a different set of die rolls and results. However such player should not be playing in the first place.
As tournament play pits a lot of unknown opponents, new gamers, and players from the computer game environment (reverting to save, anything is legal vs AI opponents is the accepted norm). Additionally awards and titles may be at stake. In this setting, use of an internet die roller is recommended. These give the additional benefit of not needed to suspect extreme die roll results. One neither has to feel guilty about great die rolls or be wary of bad ones.
NOTE: This old standby has been decertified for VIP ladder play due to reoccurring identical die sequences and should not be used.