Gross Pay Modification

Hi Gurus,

I need help again.

For certain group of employees, there is a condition where in 12% of the gross pay for THAT pay-period is added and this is the total gross (upon which taxes will be calculated). For e.g.: Say $200 is the gross earning (because he worked 10 hours for $20/hour). Now, 12% of 200 which is 24, is added and the total gross for that pay-period becomes $224. This $224 is then taxed. Can you please help writing a rule for this condition and where will you insert the same in the schema.

Thanks for the help,