how can we setup currency according to country

Hi,
We have our base currency set in Pakistan Rupee (PKR).

Scenario:
If a customer is from Pakistan than the customer is shown prices in PKR and also checkout in PKR.

However, if a customer is from US, UK, AUS or any other country than we want to show them products in their respective currency and checkout in USD

Can you help us set this up?

Currently when customer checkout the currency defaults to PKR irrespective of which country they are from.