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 $221.79   9.546%   $242.9621   $242.96   $242.95   $243.00  
  Purchase #2 $188.87   12.522%   $212.5203   $212.52   $212.50   $212.50  
  Purchase #3 $162.44   4.541%   $169.8164   $169.82   $169.80   $169.80  
  Purchase #4 $245.27   8.853%   $266.9838   $266.98   $267.00   $267.00  
  Purchase #5 $173.97   7.743%   $187.4405   $187.44   $187.45   $187.40  
  Purchase #6 $158.58   7.215%   $170.0215   $170.02   $170.00   $170.00  
  Purchase #7 $171.46   10.132%   $188.8323   $188.83   $188.85   $188.80  
  Purchase #8 $17.97   8.796%   $19.5506   $19.55   $19.55   $19.60  
  Purchase #9 $46.78   12.504%   $52.6294   $52.63   $52.65   $52.60  
  Purchase #10 $56.75   11.447%   $63.2462   $63.25   $63.25   $63.20  
  10 purchase totals = $1,443.88       $1,574.00   $1,574.00   $1,573.90  
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?