What is the theoretical probability of rolling all 5 dice on the same number?

How many favourable outcomes are there when rolling 5 dice?

The theoretical probability of (for example) rolling 5 ones is 1 / (6^5) or approximately 0.013%. Because it doesn't matter which number we get five of we can multiply it by 6 to get 1 / (6^5) or approximately 0.077%.