You can always ask your waitress.
It may be different where you live. Here, she will get it right on the spot.
There is a law, if the waitstaffs tips and wage doesn't equal up to minimum wage, the owner must make up the difference.
This sums it up. The owner is using tipping as a subsidy, and counting as though they are HIS money right from the outset, forming part of his running costs, the wages.
Customers in general do not know much about how things work behind the scenes, they are merely playing along with what has become normal. It's normal for politicians to be on the make, but it doesn't make it RIGHT.
Here in the UK, our MPs recently got a very rude awakening. It was revealed that they were using the lightly regulated "expenses" scheme to make personal profits at the expense of the taxpayer. Expenses are meant to cover what you might spend of your own money in the course of your work, they are not something you should be manipulating for profit. Even after the big shakedown, some MPs still just don't get it.
In the service industry, it is the owners who are on the make, and the government has made sure it gets it's own cut, rather than doing what it should and outlawing the reliance owners place on tips to make wages up to the legal minimum. It should be minimum wage + tips, and only staff who work directly for customers should have a share in the tips. It should be the responsibility of staff to declare what they actually make for tax.
I expect the government have brought out taxation rules on tips because they know damn well that owners are "on the fiddle" by paying sub minimum wage "on the books" and making up the difference from cash tips not on the books.
It may take a clever lawyer, but maybe one day someone will challenge the government over this and use as their core argument that tips have always been gifts, and the current accepted tax regime is not actually underpinned by any proper legal definition of tips.
If a tip is a gift, it should not be taxed.
If a tip is part of the price, customers should be made aware of this price before they order, not expected to pull a figure out of their ass as to what the correct price is when they leave.
At worst, it will result in the honesty of tips being placed on the bill as a set "service charge", something you often see here in the UK, but consumer advocates have made it clear that unlike the prices laid out on the menu, we have the right in law to refuse to pay the service charge if we feel something was lacking in the experience. As Brits, most don't want to make the necessary fuss, so the restaurant gets to keep the money even if the service is mediocre.
As for the rest, we are brought up to say "thank you" to staff who serve, not give them extra money. The thanks is the reward for good service, happy customers who will come again. If we do tip, we expect it to be a private arrangement, nothing the owner nor taxman should have a stake in.