Perhaps you could do it this way. Have a HashMap<Integer,Integer>. They keys would be the actual sum possibilities. The values would be the number of times you rolled that sum. You could do this thousands of times. The key for the sum 3 might have 30 times. The key for the sum 10 might have 300 times. You could also do it with an array. The indices would be the sums and the values would be the number of times you rolled that sum. You would ignore indices 0, 1, and 2 since those are impossible sums. To double check everything, the sum of each sums count should equal the number of times you threw the dice.
If you try to to show more information than that(e.g. what the values of the dice were or weren't) the tables would get cumbersome. Nor am I certain how you would do that.
Regards,
Jim