Starting next week iPhone owners will not only be able to buy your triple-venti-extra-hot-no-foam latte using Starbucks' mobile app, you'll be able to tip your barista for making it as well. The king of coffee is updating its app March 19th to add digital tipping for the first time and make the app easier to navigate. If you're not paying attention in line, a new "Shake to Pay" feature instantly loads your Starbucks card up from anywhere in the app. After you pay, you'll get a push notification encouraging you to drop between 50 cents and two bucks in the store's virtual tip jar. Tips can be adjusted for up to two hours after you leave (in case that macchiato really makes your day), and every purchase is saved in the form of a digital receipt you can access later on.