In our Indian store the INRs are being used only as a display currency. However on the Order Review Page there is always a message saying we will charge your CC in USDs, and the amount. The USD amount is calculated based on the FX rate.
For example for 3104 INR it says 50.37 USD which matches the FX rate. Wasn’t there any tax applied? You can PM me your order # and I’ll take a look into that.