What is the percent distribution of US surnames by letters of the alphabet?

A web site given in Related Links (below) is one of several that provide frequency information on US surnames. It claims to use information from the 1990 U.S. Census and lists 18839 last names in percent frequency order (comes in groups of 1000 to 4000 names per page). The counts are a bit squirrel because they apparently did the counting of each name, then calculated the percentage, rounded that percentage to 3 decimal places and then reversed the process and calculated the number of each name by multiplying the rounded off percentage times the grand total. This makes the counts to be the same for large groups of names... i.e.: there at 11 last names that are listed as having 92,019 people with that name because the percentage rounded to 0.037. Strange that they could not keep the exact count for each name even if they rounded the percentage. It is even more obvious for the least common names at the bottom of the list... The last 11340 names are all listed as being 0.001 percent of the total and that then is calculate to all of them having a count of 2,487. The Counts, sum to 197,955,252, but the percentages sum to only 79.596%, so there are many very low frequently used names missing from the list.