Round up total for donation at checkout on Woocommerce/BigCommerce/Shopify

We are looking to add a checkbox (automatically checked) at checkout that applies a $0.99 (or custom amount) donation to a 501(c)(4) organization we are affiliated with. A script or plugin is needed to accomplish this and we would need one or more of these to integrate with Woocommerce, BigCommerce, and Shopify. We have websites on each of these platforms, so we can add it and test for each one.