In order to work with tax inclusive prices in your WooCommerce store, just follow these steps:
  1. Go to WooCommerce > Settings > Tax > Tax options.
  1. Select the option Yes, I will enter prices inclusive of tax for the field Prices entered with tax
  1. Select the option Including tax for the fields Display prices in the shop and Display prices during cart and checkout.
  1. Click Save changes.
  1. Confirm that WooCommerce > Settings > Tax > Standard rates are set correctly for your country.
  1. Enter the standard rate for your store's jurisdiction. For example, if your store is based in Australia, you  must set up 10% GST. WooCommerce will use this information to determine the taxable base of your product prices. 
  1. Click Save changes
Add your tax settings for tax-inclusive pricing.
Add your tax settings for tax-inclusive pricing.

The WooCommerce system WILL automatically work through and adjust your database pricing but it will take time to complete.