Hi,
To get the currency rate you can use the following URL:
https://query.yahooapis.com/v1/public/yql?q=select%20%2a%20from%20yahoo.finance.xchange%20where%20pair%20in%20%28%22USDINR%22%29&env=store://datatables.org/alltableswithkeys
However, there is not an explicit way to do it, you need to implement a very specific equation to get the XML structure synchronously, and extract the currency rate from it; and finally, apply the currency rate to the rest of the equation.
The code to implement all this logic is independent of the plugin’s code, you should to do it directly with JavaScript, or using a framework like jQuery.
However if you need additional help implementing your project, you can request a custom coding service through our private support page:
https://wordpress.dwbooster.com/support
Best regards.