You may already have a tax table set up on eBay directly, this will sync with the eBay channel in Shopify or the settings may be added and edited from within the channel
To access the tax settings, select eBay → Account → Sync settings
On the next page, if you already have a tax table set up on eBay, select Force Sync from eBay and the settings will import from eBay.
To set up a new tax table or edit existing, add or remove the details on this page, then save. Once saved, your eBay tax table will update and the listings published to eBay, will automatically update to use the new settings from the table.