I'm surprised that no one was able to answer that. When I was taking Psychology class in college, the professor told us people somehow tend to ignore the digits after the decimal point. So that psychologically, 9.99 looks as if it's only $9 something, even though the true difference is only 1 penny from $10. So if you buy a bunch of stuff all ending with .99, then 10 items will be $10 difference. 终究的目的是为了让顾客多消费。As for why 黑人喜欢喝蓝颜色的酒,我特地去问了一个老黑同事，他也不知道。