Sales Tax Rounding Errors

I have a very specific problem. All of my sales prices include the sales tax so that I don't have to deal with change. When I have a sale for $60.00, the service price is $56.08. This always rounds up to $60.01. If I change the service price to $56.07, the total changes to $59.99. In this instance I end up having to adjust the final sales tax by a penny, up or down, depending on the service price, to make the total be $60.00 even. This workaround is small and doable for the most part (even if it is annoying) but when I have a credit card sale and don't catch the error, I will tell my clients there is an extra penny on their sale. But when I looked at the merchant account, there was no extra penny. So the sale went through fine, but the invoice in QBO still shows it's off a penny. In order to keep my books accurate, I tried to change the sale to accurately reflect the total, but the card was already processed so I couldn't change the invoice amount. How do I change the customer's invoice without deleting the sale? If I delete the invoice, won't that delete the credit card info? Will that do anything to the transaction in the merchant account? There was no error on the actual sale, just the invoice in QBO.