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 $164.47   8.337%   $178.1819   $178.18   $178.20   $178.20  
  Purchase #2 $241.88   3.258%   $249.7605   $249.76   $249.75   $249.80  
  Purchase #3 $32.68   3.443%   $33.8052   $33.81   $33.80   $33.80  
  Purchase #4 $46.63   7.570%   $50.1599   $50.16   $50.15   $50.20  
  Purchase #5 $134.28   13.685%   $152.6562   $152.66   $152.65   $152.70  
  Purchase #6 $146.70   13.720%   $166.8272   $166.83   $166.85   $166.80  
  Purchase #7 $238.82   6.102%   $253.3928   $253.39   $253.40   $253.40  
  Purchase #8 $13.60   6.461%   $14.4787   $14.48   $14.50   $14.50  
  Purchase #9 $227.93   3.739%   $236.4523   $236.45   $236.45   $236.50  
  Purchase #10 $229.51   7.534%   $246.8013   $246.80   $246.80   $246.80  
  10 purchase totals = $1,476.50       $1,582.52   $1,582.55   $1,582.70  
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?