Survey Results

I'm attempting to calculate results of a survey where users rate questions from 1 to 5. I've received almost 4,000 responses and am attempting to calculate percentiles from them (10th, 25th, 75th, and 90th). There are more than a dozen questions to the survey, and I'm not clear on why, but all of the percentiles for each question are the same and are also whole numbers. This is puzzling me because the averages of each question aren't identical. So, how can a question with an average of 3.29 have exactly the same percentiles as a question whose average is 3.91?