Your personal exemption. Use this calculator to determine the Total Number of Allowances to enter on your Massachusetts Tax Information in Employee Self-Service.The two most important documents for Massachusetts sales tax exemption are the ST-2 and the ST-5. If the allowable Massachusetts withholding exemptions are the same as being claimed for federal income tax purposes, the employee should complete Form W-4 only. It provides essential information on how to fill out tax withholding exemptions. Use this form to inform your employer about your tax withholding preferences. Acceptable Exemption Form: M-4. Self-Service Web Portal: Use our exemption certificate self-service web portal (Avalara Cert Express) to complete and submit sales tax exemption forms. The form is informational and should be used to complete a Schedule HC form with your MA tax return. 41C, 41A, and CPA applicants must submit a tax return.