Yes, you are able to set a store wide discount. You will need to log into your account and on the left hand side you will see a gray column with several options. Click on Settings and you will be brought to a new page. You will now be in your store settings. If you scroll down the page before you get to your shipping collection address you will see "Enable store wide discount". Click the box to enable the store wide discount and 2 options will appear. You will then be able to choose the minimum order amount that the discount applies to and what percentage you wish to offer. After you decide this make sure to scroll to the bottom of the page and click on Update Settings.
**Make sure that you remember your store wide discount will stay active until you log back in and unclick "Enable store wide discount".