Compromise.

Building a wheel is a compromise, unless you happen to have a perfectly drilled hub, and perfectly round rim. The first is fairly easy to obtain; the latter, difficult...especially with less expensive metal rims.

You can make a choice, then--do you want a
-perfectly balanced wheel in terms of tension that might be slightly out of true/round?
-a wheel that prizes roundness over lateral trueness, while still holding even tensions to a higher standard?
-the inverse of the above?
-a wheel that ranks trueness/roundness above perfectly equal tension?

In my opinion, tension that varies on some spokes (not the average, mind you) by 5-10 kgfcm is not an issue.