Philadelphia City Tax?

Calling all resources who deal with (nasty) Philadelphia city taxes....

The short comment - we generally do NOT withhold any type of local or city taxes on our employees. However, an employee has requested Philedelphia city taxes be withheld from his pay. I've done the requisite set up, and upon testing, the calculation is 3.928% of his gross income, which is a figure I did find on the City of Philadelphia Dept of Revenue website.

A lot of explanation for my question - can this city tax be overridden, either as a percent or a replacement amount? Should exemptions and/or marital status change the 3.928%

Any time the word tax and the state PA are mentioned in the same conversation, I run.

Thanks for any info on this -