Tax fraud is not always a crime. Sometimes, the very same action can be treated as a civil offense rather than a criminal offense. If the IRS decides to hold you responsible for civil tax fraud, they can assess a penalty of 75% of the underreported tax.
If you face this penalty, you will not go through a criminal court case, but you can appeal the penalty to the Tax Court. Then, the Tax Court can either uphold the penalty or remove it. Sometimes, they may reduce the fraud penalty to an accuracy-related penalty or a negligence penalty for a gross valuation misstatement.