I know Magento rounding issues have been covered a thousand times over, but I can't seem to find an answer to my specific problem.
So I'm using Magento community ediiton 22.214.171.124 with a 20% tax rate. The site works fine, right up until I try to use certain percent discount codes. The most recent issue is with a £399.99 product when a 30% discount is used.
The weird part is that it displays perfectly on the frontend; £399.99 - 30% = £279.99. This applies to both the basket and checkout stages. The issue comes when the customer actually places the order, which gets created in Magento with a grand total of £280.00.
The biggest problem with this is we use 3D secure payments, so because these 2 amounts are different, it causes the payment to fail.
I can't work out why the amounts are different in the frontend before the order is placed (£279.99), then in the backend after the order is placed (£280.00)?
Any help would be much appreciated.