you can either store the currency names with their value in database. for this approach you require to set any one currency as your default currency. i.e. INR as your default. and then save the conversion formula's for each currency from INR to them.
now when you receive the amount in dollar, convert into INR and then convert to any other currency you want. same will be the case for PKR. convert PKR to INR then to any other currency. i.e. USD
"using this approach you may need to make timely changes in formulas, as per currency rate changes"
secound way is to use already built services. one of the example is
http://www.webservicex.net/CurrencyConvertor.asmx[
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its good to write your own for personal experience but you can use third party services as well.
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