Reverse Pricing is the procedure through which the customer is allowed to offer his/her requirements to the seller for bid. In this process the seller is not marketing a product to the buyer but the reverse is happened.
For Reverse Calculations
Go to T-Code V/06 & open any Condition Type.
Under Claculation Type there is one option - H - Percentage included.
The % can be calculated in two ways :-
1) when the base price is not inclusive of %, if the base price is 100 and tax rate is 5%, then the calculation will be as follows :
100*5 / 100 = 5
in this case amount of tax is Rs 5.
2) When the % is included in the base price (as your case is), the same calculation will be like as follows :-
100/105 *100 = 95.23
and the tax value is 100 - 95.23 = 4.76 insted of 5 this is what is the reverse calculation.
In SAP both the situation can be handled from Calculation type of a Condition type in V/06. If you want to calculate the value of a % as in case 1 then select "A" in calculation type and if you want to calculate the value of % as in case 2 then select "H" in calculation type of the Condition Type.