Zend certified PHP/Magento developer

Complex multisite product entry with different tax rules

We are setting up different stores with own product entry, metric system, currency, etc.
Like US, EU, UK. All products should be displayed on every store view, displays depending from location.

Challenge here is that a product entered within US store should reflect local tax if delivery address is within US. But on other sites it reflects excluding VAT.

However, how to deal if there is a combined order with products from both EU as US, in terms of;

  • tax calculation
  • shipping calculation

Is there any recommendation how to deal with this?