Import goods value at current exchange rate or payment rate?

Hello,

We import goods valued at 5% and 14.5% vat rate.

we purchase goods from china on 1 month credit basis and make payment in dollars through our bank.

Usually, when we receive goods, we calculate the value of goods as per the custom clearance dollar exchange rate and add up all the custom duty, service charges, forwarding charges etc and keep some percentage and sell the goods.

After one month, we pay the payment for that goods through our bank as per dollar rate which is different from what we entered in our purchase books, so how do we calculate that as per accounts and where is the difference of amount in dollar rates then and now will effect?

For Example :

Goods imported on 01.04.2013 with invoice value of $10,000 all are taxable at 5% VAT in india.

1.4.2013 dollar rate = 55.75

So we total that to 5,57,500/-

Expenses Incurred such as

Customs Duty=2,00,000/-

Clearing Charges=15,000/-

Freight Charges=35,000/-

Labour Charges etc =20,000/-

Total Expenses are Rs.2,70,000/-

So, its almost 48.45% expenses on total purchased goods.

Therefore, we added 48.45% expenses to all goods to get the cost price per item as per indian rupees.

we sold by having 5% to 10% profit and sold the goods.

Thereafter, on 1.6.2013 we made a payment of $10,000 through bank at the rate of 58.75 and bank charges of Rs.1500/- totalling upto 587500 + 1500 = 589000 which is Rs.31,500/- more than what we entered in our books and sold as per that rate.

so where does that 31,500/- will go and was the method of calculating the amount of goods is right?

kindly suggest new method or idea to make accounts with above example.

Thanks & Regards