Conditional Formatting?

Hi folks!

I'm trying to create an expense report of some type. 

Here's what I'm trying to accomplish...

I want to be able to put in the total value of a charge in column F. Then, I want to be able to select the currency type from a drop down menu I've created in column G. What happens in column H and I will depend on the currency that is chosen from the drop down menu.

If CAD is chosen, I would like Column H to multiply the value in column F by the tax rate and then Column I will add the two columns together.

If USD is chosen, I would like column I to simply multiply column F's value by an exchange rate I input (1.277 for example) and populate the new total in CAD.

If euro is chosen, I would like the same thing as above but a different exchange rate. 

I have a reference sheet set up with the applicable exchange rates already, thinking I would maybe use LookUp or something...?

Any thoughts if this is even possible?