Go to Products and filter for the items you want to update.
Once selected, click on the Actions tab and click „Bulk Update Prices”.
On the opening lightbox, you can select if you want to update the Buy It Now (BIN) or Auction (Starting) price, and if you want to update the variation prices as well.
Then you can select if you want to add, deduct from the price, or make the prices equal to a certain amount.
Also, you can select if you want to increase your prices with, for example, 5 GBP or 5 %.
After setting the rounding up rules, you can click to update the selected items. Don’t forget to revise them to show on eBay too.