From the Accounting App, visit:

Configuration --> Accounting --> Taxes

This lists all Taxes setup in Odoo.

From the Filter menu below the search box (click the magnifying glass at the right end of the search box if you don't see the Filter menu) make sure just the Sales filter is selected.

Open each Sales Tax record to review and make sure the account is set properly:

(RIGHT CLICK this image and select VIEW IMAGE or OPEN IMAGE IN NEW TAB depending on your browser, to see a larger version)

The field highlighted in RED is where you set the Account, and below is where you set the account for Tax Refunds (recommended to keep it the same).