How to toggle price display with and without tax? In Europe  it is normal for trade suppliers to show prices exclusive of VAT, but for retail suppliers to display prices including VAT. 

For the use case where merchants who supply both trade and retail. Many e-commerce sites have the option to toggle the price display to show values with and without tax.

See https://www.tool-wise.com/ (radio button, top right)

Does such an option exist for Drupal Commerce? I haven't found anything in contrib.
Check out commerce price by components module. You can show both prices with and without VAT. If you want to toggle I'm afraid you will have to write a custom module... .