Let's do some math ..  Rounding examples of 10 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $19.99   7.540%   $21.4972   $21.50   $21.50   $21.50  
  Purchase #2 $114.36   10.248%   $126.0796   $126.08   $126.10   $126.10  
  Purchase #3 $61.82   11.498%   $68.9281   $68.93   $68.95   $68.90  
  Purchase #4 $193.29   7.174%   $207.1566   $207.16   $207.15   $207.20  
  Purchase #5 $171.47   6.238%   $182.1663   $182.17   $182.15   $182.20  
  Purchase #6 $137.53   11.111%   $152.811   $152.81   $152.80   $152.80  
  Purchase #7 $122.47   13.309%   $138.7695   $138.77   $138.75   $138.80  
  Purchase #8 $164.26   4.537%   $171.7125   $171.71   $171.70   $171.70  
  Purchase #9 $213.37   9.556%   $233.7596   $233.76   $233.75   $233.80  
  Purchase #10 $45.38   12.699%   $51.1428   $51.14   $51.15   $51.10  
  10 purchase totals = $1,243.94       $1,354.0232   $1,354.03   $1,354.00   $1,354.10  
Come on folks.. this just does not make any cents. We got rid of the 1/2 cent back in 1857.. Getting rid of the 1 cent coin is way, WAY past due. The penny has become a social and cultural anachronism. If our friends in Canada, Australia and a dozen other countries can stop the use of their pennies, why can't we?