Exchange all button for currency exchange

As an experiment I purchased loans in a different currency. Now these loans are paid back and I would like to exchange all the available amount back to my default currency.
Unfortunately this is not possible because there is a tiny amount left which can not be exchanged. I am guessing the problem is that loan returns are calculated with more decimal places than the exchange.
Could you implement an „Exchange All“ button?
Also after all remaining amount is exchanged and no loans are left in one currency I would like the interface to go back to one currency mode without the tab-bar for currency selection so it is a more clean look and not cluttered with currencies which are not in use anymore.

Thanks
Josh