You know, don't push the button, don't push the button, don't push the button, and then some socko finish. I was pleasantly surprised by how the book bobs and weaves and is a lot more active and entertaining that just that. MILD SPOILER, so don't tell your four year old.
The late payment penalty applies to any portion of your federal tax that remains unpaid as of the due date, typically the tax filing date. The IRS imposes a failure-to-pay penalty of one half of one percent for each month or part of a month that the tax goes unpaid.
Imputed income is not subject to federal withholding, so you are not paying taxes on that amount out of your weekly paycheck. Just because imputed income is exempt from withholding, that does not mean it is exempt from federal income taxes entirely. You must include the amount in your total adjusted gross income at the end of the year.