If you want to use Google Shopping, yes the product landing page needs to be the same as the data feed. So using multifeeds will not fix your product landing page issue, but it will allow you to add the vat to the prices.
As Google crawls from anywhere in the world, you will need to show prices inc vat regardless where the users is located.
This issue, is commonly misunderstood with users from the UK, that want to show ex vat to other countries.
So instead, the correct way is to show ex vat, based on query strings, not ip based.
This can be done, when appending the query string ?currency=USD
Then show the correct price based on this, not based on IP, that is the correct and only way forward.