Custom reports are way to go. In the latest version (20.8.61) I exposed a few more fields such as currency and account amount.
So here is how it would work.
Let’s start with list of customer invoice totals in base currency:
But you don’t want base currency, you want to see totals in customer currency. Just change Amount to AccountAmount so it’s like this:
Now you will see it’s still not useful because customers across multiple currencies are mixed together. In other to group them by currency. Check the Group By... button and group them by AccountCurrency like this:
This will group your sales invoice totals by customer currency.
This can be achieved by simply checking Groups to collapse to hide transaction-level details and just show totals for your groups.
But I still recommend not to group to collapse so you see what specific transactions made up your totals.