VAT inclusive price
A VAT-inclusive price is the net multiplied by one plus the rate. A net 49.50 at 21% displays as 59.90, and consumer law in most of Europe requires that inclusive figure to be the prominent one.
How to set a VAT inclusive price
Rounding to a nice inclusive figure is where the net quietly changes. Deciding to display 59.95 rather than 59.90 lifts the net from 49.50 to 49.55: trivial per unit, but it means your price list and your accounting figure disagree unless you update both. The usual practice is to choose the inclusive price first, since that is what the customer sees, then let the net fall out of it rather than the other way round.
Questions
To consumers in the EU and UK, yes; the inclusive price must be the prominent one. Business-to-business price lists may show net.
Pick the inclusive figure first, then divide by 1 plus the rate to see the net it leaves.
Usually yes, at the rate of the goods being shipped. Mixed baskets apportion it.
Show both figures, with the inclusive price prominent for consumers and the net clearly labelled.
Either the price changes or your margin does. A rate rise absorbed rather than passed on comes straight out of the net.