I have an issue where a supplier provides goods and they total invoices which are Ex VAT. The invoice then has a VAT total breakdown at the end of the invoice. Due to the way they work there discounts it can lead to item prices to the 4th decimal place £0.0000, this may not be a problem rounding for one or two items, but when you have dozens of items with an extra half penny it adds up and throws the totals out. This then requires extra work using a calculator to manually manipulate every invoice line total, multiplied by the VAT amount then adjust the line total accordingly.
Solution: Provide the ability to switch invoice line totals to EX VAT or VAT amounts per invoice/customer.
It would also combat the issue where suppliers give random discounts for promotions on items where the discount causes multiple decimal point prices.