Integrate a round up option to donate to a charity in the cart of my website

I am looking for a developer to integrate a charity round up option in my Shopify website cart drawer. The idea is to offer to our customers an opportunity to donate to a charity by adding one pound or more to their order's total amount. Here's an example website that has this similar option in their cart: https://www.blueland.com/. I attached a screenshot of their cart where you can see exactly how I would like it to look like in my website.