> will I be punished with an iron fist if I'm a couple bucks off?

This is a common misconception with the IRS.

The IRS is more like a very understanding parent.

Understanding parents know that their children are going to mess up. Understanding parents are not out to deliver punishments out of joy/fear. Understanding parents just want their children to follow the rules.

The IRS is very reasonable. The IRS wants to work with the Taxpayer.

Just don't do illegal things like intentionally evade the rules.