The difference in annual earnings is $6240 -6220 = $20. 20% of that is $4. There are 24 semi-months in a year, so the difference in amount deducted is about
.. $4/24 = $(1/6) ≈ $0.17
If the payroll department is paying attention, the difference in deducted amounts will be $0.16 2/3 over the year. Some paychecks, it will be $0.16, and others it will be $0.17.