In receipts, reports, and quick estimates, rounded tens can be easier to work with than exact numbers. Write a function round_sum that takes three numbers a, b, and c, rounds each one to the nearest multiple of 10, and returns the sum of the rounded values. If a number ends in 5 or more, round it up; otherwise, round it down.

def round_sum(a: int, b: int, c: int) -> int: