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 $246.28   13.400%   $279.2815   $279.28   $279.30   $279.30  
  Purchase #2 $122.56   8.162%   $132.5633   $132.56   $132.55   $132.60  
  Purchase #3 $26.46   10.487%   $29.2349   $29.23   $29.25   $29.20  
  Purchase #4 $13.27   12.831%   $14.9727   $14.97   $14.95   $15.00  
  Purchase #5 $116.96   4.218%   $121.8934   $121.89   $121.90   $121.90  
  Purchase #6 $145.37   3.471%   $150.4158   $150.42   $150.40   $150.40  
  Purchase #7 $63.66   4.414%   $66.47   $66.47   $66.45   $66.50  
  Purchase #8 $158.79   8.348%   $172.0458   $172.05   $172.05   $172.00  
  Purchase #9 $196.38   11.236%   $218.4453   $218.45   $218.45   $218.40  
  Purchase #10 $110.28   13.363%   $125.0167   $125.02   $125.00   $125.00  
  10 purchase totals = $1,200.01       $1,310.34   $1,310.30   $1,310.30  
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?