I believe what you're after is: https://github.com/CartThrob/addon-multi-location-settings-manager
Found via this forum post: http://cartthrob.com/forums/viewthread/4884/, and this one: http://cartthrob.com/forums/viewthread/4622/P15/#28813
They look a little outdated (last update 2 years ago!) so don't know how relevent it is to the current release.
Check you haven't got a hidden input in your checkout form process. This can overwrite the currency. If its in there, remove it, or change the value. It usually works like this:
<input type="hidden" name="currency_code" id="currency_code" value="CAD">
Not sure what that add-on your using is. But the way I recently got around this was to set the ...
Store currently only supports charging cards in a single currency per site which you set in the Store > Settings > General tab in the CP. Lets say that you have it set to USD and your customer is from England and therefor is paying with British Pounds. The payment gateway will convert the currency so that you collect the correct amount in USD.
It is possible using the Stripe gateway and hacking the build_payment_request method in the PaymentsService class.
You'll want to change this line:
$request['currency'] = config_item('store_currency_code');
to accept a POST variable:
$request['currency'] = $this->ee->input->post('currency', true);
Once you've done that, you should be able to ...