Okay, so there's lots of confusion here. But from my experience of doing my own taxes for 20years, having a CPA that specialized in business taxes as a parent, and google...(disclaimer: I'm in Ca, and not a CPA myself)
Your tips received are "taxable income". This is true of almost any money you get in life. Small amounts of income may be taxed, but not at the full rate.
Starbucks will be declaring your digital tips and withholding the applicable taxes on them. Your in store cash tips will still be distributed as usual.
Tips are (US federal) ONLY taxed if it's more than $20 per day. (Edit:per MONTH) Because your digital tips are already covering your butt, your cash tips are essentially untrackable by the IRS. Therefore while you 'should' manually declare your cash tips, you actually don't 'need' too.
Tldr: (edited) Don't bother with tracking them.