To move your Round-Up widget elsewhere on the cart page, first switch from Automatic to Manual placement:
Then copy the code snippet and manually paste it where you want it to show (within your code files):
To place it in the Cart page below the cart, most likely you'll want to paste the code snippet below the closing </form> code in your cart-template.liquid file:
Remember to save your changes! Then go to your Cart page to find your Round-Up widget below the cart.
Email us at firstname.lastname@example.org for assistance.