No matter what I enter for car registration fees it isn't affecting my federal tax due

[amysea]

I saw the answer for the same question posted a year ago, which said it's because the standard deduction was used.  But in my case I know the itemized deduction was used.  If I change the charity donation amount, the tax due/refund is affected.  Why is that?

[KrisD · Accepted solution]

If you are subject to the Alternative Minimum Tax (ATM) certain deductions will not be added, such as taxes paid, but some deductions are allowed, such as charitable contributions.