I live in a country where the tax is always included in the price, and tipping is not seen as mandatory. So the price on the tag is what you pay. So I may be a bit biased in my "hate" for how it's in some countries, because I'm always taken by surprise at the register.
Yeah, I'm not saying that I like it, just that I understand the motivations involved. On a purely rational basis, it should make no difference (as the end-price ends up the same), so sellers should opt for customer preference, but sadly, we are not fully rational creatures.
It does make a tangible difference in the cash economy though. When the price tag includes tax, the prices are generally set to easy multiples of the currency. Fewer coins to cart around and manage (and no give/take a penny trays). I found it amusing in the US when I went to McDonalds and ordered three things from the 'dollar menu'... and was charged $3.24. I also found it odd that a few Americans, despite living in this system their whole lives, had trouble in predicting their costs at the register.
Here in Australia there's a 10% sales tax, included in the original price. For anything above a few dollars, most prices are whole dollar amounts, and the vendor sets aside 1/11th of the price for the sales tax. What you actually pay is easy to manage and predict, though you get a receipt specifying the tax with odd numbers (due to the 11ths). Go into a supermarket and buy a carton of Foo for $2.69? It's $2.69 at the register.
My gut tells me that this is why Americans are so much more vocal about tax - sales tax is a stone in their shoe. It's addition at the register makes things unpredictable (not to mention any sale that crosses a border somewhere). Here it's streamlined away, and there's no cognitive weight borne by the consumer at all.
What really makes sales taxes fun in the US is that they are variable in many states. If I go to my local Walmart at the start of the school year, some items I pick up may be tax-free because they are considered school supplies and there's a "sales tax holiday", others items are considered "Groceries" and will be taxed at a reduced rate, but prepared (hot) foods, booze, and non-food items are taxed at the full rate.
Then there are the cities and counties that have additional sales taxes.
When I lived in Germany it took me about 5 minutes to fall in love with prices being listed inclusive of taxes.
And on that note I think part of the difference in reaction is down to expectation. Americans don't like being "surprised" at the register either, but in the case of sales tax and tipping there is no surprise; it is assumed that will happen and factored accordingly. But if you surprise me with a $.99 dessert on my bill that I didn't actually ask for, you can bet your ass I'd raise a problem about that at the register.
