We enter our product prices into magento exc vat and display them inc vat.
To get a nice price displayed to the customer as 19.95 the exc vat (20%) price would need to be 16.625.
If we store the price in the database directly or use magento store manager importer we can import the product price to be 16.625 but within the admin of Magento the price gets rounded up to be 16.63 and then when the tax is worked out the total would be 19.956 which then gets rounded up to 19.96
Referencing this other question Round Price to 4 decimal places it seems to do the trick on the surface but it seems really dangerous as it could have a knock effect with other areas of the store, specifically the checkout and payment gateways. Has anyone else encountered this issue or can offer a suggestion?