All the numbers in the expression are odd numbers.
Any odd number multiplying 5 will end up to have 5 at the ones digit.
For example, 1 x 5 = 5, 3 x 5 = 15, 7 x 5 = 35 …
Thus, the product of all these odd numbers in the expression is an odd number and is a multiple of 5.
So the ones digit of the above expression is 5.