I'm going to round.

Top 1% of Americans pay 40% of all Individual Income Taxes.  Top 1% has 22% of AGI (Adjusted Gross Income)
Top 5% of Americans pay 60% of all Individual Income Taxes.  Top 5% has 37% of AGI
Top 10% of Americans pay 71% of all Individual Income Taxes (IIT).  Top 10% has 47% of AGI
Top 25% of Americans pay 86% of all IIT.  Top 25% has 68% of AGI.
Top 50% of Americans pay 97% of all IIT.  Top 50% has 87% of AGI.
Bottom 50% of Americans pay 3% of all IIT.  Bottom 50% has 13% of AGI.
Just for fun:
Bottom 75% of Americans pay 14% of all IIT.  Bottom 75% has 34% of AGI.

Look two things are clear here.  1) The rich provide the lion's share of the tax revenue of IIT.  2) Bottom 50% have only 13% of AGI which is not great.  Our GINI coefficient is .45, or 45.  I'd like to do this later: see if there is a statistical significance between countries per capita rate of saving AND the gini coefficient.