Which document would a taxpayer use to dispute an IRS audit finding?

A taxpayer would use Form 843 to dispute an IRS audit finding because this form is specifically designed for requesting a refund or appealing IRS decisions regarding various tax issues. It can be utilized to appeal certain penalties or taxes assessed during an audit, as well as to claim a refund of overpaid taxes. This makes it the appropriate choice for a taxpayer looking to formally dispute the findings of an IRS audit.

The other options do not serve this purpose. Form 1040 is the standard individual income tax return, while Form 8862 is used to claim the Earned Income Credit after it has been disallowed. Form 8889 is related to Health Savings Accounts and does not pertain to audit disputes. Thus, among the provided documents, Form 843 is uniquely suited for addressing audit findings and initiating an appeal process with the IRS.