We need to add a "TIP" to our shopify shopping cart, we need the customer to be able to choose from a "% of total sale" or "Hard number". We are looking to pay a one time fee, so no monthly subscriptions. We would also like some sort of tech support at least for 60-90 days after implementation. Also, we are taking suggestions for a better solution for our online store that is able to process payments for wine and liquors (in NYC), has the above "tip" function, inventory integration with Bindo, all in one vendor. Please send your proposals to email@example.com.