There's some tax free employer benefits that are not subject to federal and state tax, that the locals do tax. Your year end pay stub may be a quick place to identify it. Otherwise you'll have to ask your employer. You are correct, most local jurisdictions stop at the amount in box 5.
The city tax dept web site would be another place to check.
For example, here's a list from my city's web site:
Wages, salaries and other compensation
Bonuses, stipends, and tip income
Commissions, fees and other earned income
Sick pay (including third party sick pay)
Employer supplemental unemployment benefits (SUB pay)
Strike pay
Vacation pay
Employee contributions to retirement plans & tax deferred annuity plans (including Sec. 401k, 403b, 457b, etc.)
Pre-retirement distributions from retirement plans
Profit sharing
Uniform, automobile, moving & travel allowances
Reimbursements in excess of deductible expenses
Employee contributions to costs of fringe benefits
Employer provided educational assistance, and/or reimbursement (taxable to the same extent as for federal taxation)
Royalties, if not derived from intangible property
Stock options (taxed when exercised, valued at market price less option price on the date the option is exercised)
Employer paid premiums for group term life insurance (taxed to the same extent as for federal taxation)
Compensation paid in goods or services orproperty usage (taxed at fair market value)
Excess employee discounts
Income from wage continuation plans (including retirement incentive plans, severance pay and golden parachute payments)
Income from guaranteed annual wage contracts
Prizes and gifts if connected with employment
Director fees
Income from jury duty
Union steward fees
Disability pay if received as a benefit of employment (includes third party plans)
Income received as a result of a covenant not to compete
