You could adjust the skill's hit rate to something like 50% to make it hit between 0 and 6 times, although the number of hits would center around 3 (rather than an even distribution between 0 and 6) and you couldn't necessarily tie it to the dice roll animation.
What you could do, though, is have the formula pick a random number between 1 and 6 and store it for use in a Common Event which shows the dice roll. Here, it only hits once, but the skill's damage is correctly multiplied by the dice roll.
Example formula: $game_variables[25] = rand(6) + 1; (v[n] * a.mat * 2) - (b.mdf * 2)
Example common event to be tied to that skill:
Conditional Branch: Variable 25 is equal to 1
Show Battle Animation: "Dice Roll Result 1"
End
Conditional Branch: Variable 25 is equal to 2
Show Battle Animation: "Dice Roll Result 2"
End
(etc. up to 6)
For anything that's smoother graphically, you'd probably have to script it from scratch or use some kind of graphical aid script like the Luna Engine.