Guess taxes based on IP while not being logged in
As of now, there is a disclaimer "Any applicable taxes will be calculated after you register or log in." shown above the order form when one isn't logged in yet. While this might be common practice in the US, thats not the case for the EU.
Within the EU prices are always shown inclusive of any applicable taxes to customers. In the e-commerce world this usually means that the shop initially shows you the VAT rate estimated on your IP and adjusts the price once you entered your billing details. (Some shops also just assume their country and apply their local VAT rate at first and adjust at checkout, but you never see prices without any taxes applied.)
Since you already have tax calculation support and have GeoIP support, I guess that shouldn't be too hard to implement, but would make the checkout process much more convenient. I fear using the panel as of now could create unhappy customers since the price significantly jumps up at checkout which isn't something European are accustomed to happen. (Trust me, as someone who visited the US in the past, I can ensure you: it takes quite some time to get used to applying VAT rates at checkout if you are used to system where prices are always inclusive of taxes)