me, restaurants and tips(and tax)

I have this problem everytime when I eat in a restaurant in US, we need to give them tips, its quite a complex thing seeing that it is not written anywhere, be it in the "United States Declaration of Independence", or under any law in US, its not even mentioned anywhere in the menu or anywhere in the restaurant, but they sure expect us to give them tips of 10-15% of the total amount. Especially chinese restaurant, they'll chase you down(or so I heard), how memalukan chinese people. In california, the government charge you 8.25% for all items and the restaurant charge you an additional 10-15% tips, its an unspoken rule, and that sucks ass.
I have a hard time everytime trying to calculate how much I need to give for the tips, if only I can do math as fast as I can mandi(my record time is 4 minutes 21 seconds, take as time entering the bathroom and time stepping out of the bathroom). It gets harder when you eat together with a bunch of people, not only you need to calculate the tips but you have to calculate how do you split the bill ><
Say for example, you go out and eat with 5 people and the bills comes, total is USD53.86, excluding govt tax(8.25%) and excluding tips. Make it alittle easier, we split the bill equal among all, so each person pays...................(if it take you more than 4mins20sec, then you suck at math too, ahhh ahhh ahh no calculator, u think i bring calculator when i eat in restaurant??) around USD12.86 (u give 10% tips)....not simple lerrr....
another thing is the 8.25% govt tax, that just suck donkey balls, its ok if you the items are like less than 100 dollars, say if you spot a laptop which says GREAT PRICE!! USD799, it actually will cost you around USD880, from USD799 it becomes USD880....thats a huge difference! 1st they charge you 8.25% for the tax then they charge you another 20 dollars for some recycle cost or something....so its cheat ppl wan
But well I must say, the service here are alot lot better than back at home, waiter are alot more friendlier and helpful, they smile, they greet....and yea they cal l me SIR....that works on me everytime.