My 3rd grader had the following quetion:

Abe wants each person at his party to have about 1 cup
of punch. If he invites 18 children and 9 adults,about how
many cups of punch should he make?
The teacher indicates the correct answer is 30. The
correct answer is obviously 27.30 is the rounded answer
and should be taught as ronded and not referred to as correct.
Why is rounding such a large part of curriculum? Is it
not more valuable to teach process to achieve correct answers.
As opposed to figuring out estimates?