This stuff is where I think I can help. I'm a business application software architect for enterprise-level ERP and CRM systems by day.
For the situation you're outlining, the reality is that you almost always need to capture both a operators local currency price as well as the converted to shop's default currency price in nearly every scenario. The reason is that for most backend operations, the main value than needs to be factored and used is the shops default currency value. For the front-end operations, ordering, refunds, etc, the customer's (operators) local currency value is nearly always the number needed. Plus, from the front end standpoint, knowing the customer's localized value and it's converted default value at point of entry it's vital, rather than having to go back and try and figure it out later for reporting. It's tough to know exactly when you'll need one value over the other in all scenarios, so the best practice in our development is to store both at point of data entry/change.
Now, I don't know the exact purpose of the columns mentioned above, but they seem to be servicing the backend store owner, who generally will operate within just their primary default currency.
Hope that helps.