I've recently been travelling a lot (which as my family is well aware, is a normal state!) and wanted to be able to easily keep track of the exchange rate, plus be able to calculate the prices including tax - as well as find out how much it would be in my normal currency.
Step 1 was finding an API I could use. I'm a big fan of free - and when that's nor possible affordable. Naturally XE Currency was my first port of call but that was a little out of my price range. A little Googling found Fixer.io which is free, and while not giving the identical rates to xe.com or my card company, close enough to give me a very good approximation.
The first step was creating a Workflow which would get me the current exchange rate, and save it to a file so I could use it offline. A simple GET command and some RegEx was all that was needed to extract the exchange rate, then it was a simple matter of saving the file for later retrieval - and I added an alert at the end.