Hi Srinivas
1,If you want to know the Payroll Retro Calculation happend or not after completion of payroll process you can check in PC_PAYRESULT (For Period-In Period)
2.Effect of Retro Means if SEC 89 (Check the SAP document of SEC 89 Relief) relief wagetypes will generate and same amount effect on Employee Gross salary (some cases) accordingly it will effect in Income Tax
Regards,
Murali.