How do I get a price including VAT that is spot on? 

If you sell your products including VAT, it's common to want to display round number, such as 10.00 GBP, 35.00 GBP, or 100.00 GBP.
The problem with this is that if you have a price excluding VAT with 2 decimal places, then it is sometimes impossible to get a round number. Let's take the example of 15.00 GBP.
If you take 12.76 GBP as the amount Excl. VAT and you multiply it by the VAT (17.5%), you get 14.993, which rounds off to 14.99!
If you take 12.77 GBP as the amount Excl. VAT and you multiply it by the VAT, you get 15.00475, which rounds off to 15.01!
The only solution is to use an amount Excl. VAT with 3 decimal places, or 12.766 GBP (Excl. VAT), which gives you 15 GBP (Incl. VAT) when you round off to 2 decimal places (Incl. VAT).
In each item file, you can define prices excluding VAT with 3 decimal places. To the right of each price entry field, you have access to a calculator allowing you to calculate the price excluding VAT with 2 or 3 decimal places to get the "correct" price including VAT in relation to the VAT rate.
For more information about this problem, which is more complex than it seems, click here. 
