The problem is to create a function roundSum which takes three integers as input and returns their sum. However, before adding, each number should be rounded to the nearest multiple of $10.$ If the last digit of the number is $5$ or more, round up to the next multiple of $10.$ If it$$s less than $5,$ round down to the previous multiple of $10.$

The roundSum function should accept three parameters:

a: an integer value.

b: an integer value.

c: an integer value.

Additionally, to avoid repetition, write a helper function round$10$ which will perform the rounding operation.

Here are some examples:

roundSum$(16,17,18)$ should return $60$