If you sell your products not only to end customers within the EU but also to non-End Users countries, it makes sense to display the net prices to customers outside the EU in addition to the gross prices. The same applies if you sell to commercial customers in the EU and you want to buy these customers at net prices.
This is compulsory as Shopify is a bit “unconventional” when it comes to the confirmation or VAT calculation. On the off chance that you have set gross prices and a customer from the US buys you, the VAT is effectively reported with 0%, yet the price does not change, because Shopify does not deduct the VAT.
If end customers outside the EU and business EU customers are almost certainly paying for you without VAT, i.e. at net prices, all prices must be net. At the point, VAT will not be added in the checkout and the US customer extremely just pays the net price.