Small Business Taxpayer Bill of Rights Act of 2021 This bill modifies various tax enforcement procedures and requirements that affect small businesses and other taxpayers. The bill modifies requirements regarding awarding costs and fees to small businesses for administrative and court proceedings, the amounts of damages and penalties that are allowed for violating various tax laws, dispute resolution and appeal procedures, enforcing liens against principal residences, terminating Internal Revenue Service (IRS) employees for misconduct, reviews by the Department of the Treasury Inspector General for Tax Administration, and the release of an IRS levy due to economic hardship for business taxpayers. The bill also allows a tax deduction for a portion of a taxpayer's expenses for certain audits, prohibits ex parte communications between officers in the IRS Independent Office of Appeals and other IRS employees with respect to matters pending before the officers, establishes a 10-year term for the National Taxpayer Advocate, and repeals the requirement to submit a partial payment with an offer-in-compromise to settle a tax liability.