What if the receives service charge which is not included in the enumerated exemptions such as holiday pay, overtime pay, etc., will he still be exempt from income tax? If not, how will his income tax be computed?

The MWE will still be exempt from income tax on his SMW including the other income earned specifically enumerated as exempt under the law. However, income other than those in the enumeration shall already be taxable. The taxable income shall be computed by deducting the non-taxable/exempt portion and other deductions from the gross compensation income. Then, the resulting taxable income shall be multiplied to the applicable income tax rate using the prescribed tax table to get the amount of income tax due.