Unfortunately, such option is currently unavailable. However, I would be happy to send it to our development team as a feature suggestion. We value our customer suggestions and take them into consideration in our development plan, however, please note that the suggestions may not be always implemented fully.
You can also visit our Feature Request section and post your request there.
It is not possible to refund an item without the receipt.
If the customer that wants to return an item is a registered customer, you can view their purchase history in the app and find the receipt where they have bought this item.
You can check this help article: Purchase History of a Registered Customer in the POS
You can cancel receipts in your account in the Back Office.
When you cancel a receipt, it will not be accounted for in the reports, and all items will be returned to stock.
Please, check the tutorial for more details: How to Cancel Receipts
There is the report by taxes in the Back office. All taxes there are shown separately.
However, you have to understand how the system calculates the taxes if there are a few taxes applied at the same time: How Taxes are Calculated