Use a hashMap to store the occurrences of each value:
// initialize
Map<Integer, Integer> occ = new HashMap<Integer, Integer>();
for (int i = 1; i <= 6; i++) {
occ.put(i,0);
}
and then, whenever you "roll the dice, say dice = 5
you do:
occ.put(dice, occ.get(dice)+1); // update the number of occurrences of the result of the current roll
finding the percentage now will be easy, for each "roll" it'll be:
100 * occ.get(dice) / number-of-rolls