If you have already selected the option "My taxes are not included in the product price, calculate them on checkout", then you need to know that when this option is active, taxes will be calculated on top of the order subtotal during checkout.
However, beware that you need to make sure your settings on Shopify match this setup, otherwise there might be a message "Taxes included in the price" on your store, although they aren't.
You would need to go to Taxes in your Shopify store and make sure that tax information won't be shown on your product page.
Step 1: To find Taxes options in Shopify, go to your Shopify store > Settings > Taxes.
Step 2: You will see the Taxes section. Please, make sure that the field "Show all prices with tax included" is not selected. Then, don't forget to click on "Save".
You could find more information about Taxes in the Shopify guide: https://help.shopify.com/en/manual/taxes