There is a 1/6 chance of rolling a 5, a 1/6 chance of rolling a 4, and a 1/6 chance of rolling a 6. All three numbers have to be rolled in a row for the criterion to be met.
To find the probability of rolling these three numbers specifically in a row, we must multiply the individual probabilities together:

The probability of rolling a 5, then a 4, then a 6, is
1/216, or one in two hundred and sixteen times.