Short answer... Probably. But there will be a lot of formatting to do. You can get most of that done with copy/paste, and dragging cells. Once you download Square's Template file, you can modify it (copy and paste in your inventory), in a way that is non-destructive to Square's formatting... Otherwise it won't work.

Go to Items from your Dashboard. You'll notice there is an import/export up at the top right... That should get you started.