WooCommerce Displays The Wrong Prices
The problem: After enabling caching, sometimes prices are incorrectly displayed—sometimes with tax, sometimes without.
This type of issue usually depends on your WooCommerce tax and geolocation settings.
If you have set WooCommerce to automatically display the price with or without tax, based on the customer's address, it means that you'll need to use the page-caching compatible Geolocate feature.
To do that, follow the steps here to enable this option, while making sure the site stays cached:
Pages Aren’t Cached When WooCommerce Geolocation Enabled
You can also use the plugin Tax Display by Country, by Aelia. WP Rocket has automatic compatibility with this plugin.