Default tax setting to "no tax"

Edit Subject

I use the ipad register at my bar/restaurant. We don't charge our customers tax when they only buy drinks. But, when there is a tab that has drink and food, we charge tax. More often than not, we are ringing up drinks (without tax) as customers order. It would be great to have the option for the tax button to default to "no tax" and one can press tax as needed. Of course, you would still have the option to have it default to "tax" as their are those who tax more often than not tax. I'm not suggesting that the tax button changes but simply that one can choose for the tax button to default to "no tax".
Thanks!