Calculating Percentile Rank

Thanks for any help with this. Here is the issue:

In calculating the percentile rank of a given number one finds the rank of the given number in a range of ranked numbers and reads off the percentile of that rank. There are often tie values in the range of numbers used. If the number is a tie number, sometimes people take the rank of the first tie value as the percentile, sometimes people use a calculated rank that allows for the ties.

Do people ever take the rank of the last tie value? If there are a lot of tie values it can make a large difference in the percentile. So the question is: In the event of tie values is it ever valid to read the percentile from the highest ranked tie value? I think the answer is no but I need to be absolutely sure.

Thanks very much!