Set your Home country and enter the Tax percent when editing and showing prices (If you are unsure what tax rate is being charged you can scroll to the bottom and see a listing of all countries and Tax Rates and even add a new one if needed. )
Select your Tax strategy - If you use the Simple tax option highlighted here, Simplero will determine the tax based on your client's location. So if they are in the US it will charge the US currency and tax and if they are in Canada it will charge the Canadian dollar and tax rate.