Businesses in Fairfax County are required to pay taxes on tangible properties. As a start, you need to fill out this form: Business Return of Tangible Personal Property, Machinery and Tools and Instructions.Real estate and personal property taxes can be paid at any of the following banks in Fairfax. ➢ To avoid the late filing penalty of 10 percent, a completed filing must be postmarked or returned no later than May 1, 2021, to the. If taxes are included in the property owner's mortgage payments, the City will bill the bank or mortgage company for taxes due. When you complete your registration, you'll receive your 15-digit sales tax account number and your Sales Tax Certificate of Registration (Form ST-4). Business Personal Property Tax. If October 5 falls on a weekend, the due date will be extended to the next business day.