Let's do some math ..  Rounding examples of 6 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.59   12.405%   $66.9821   $66.98   $67.00   $67.00  
  Purchase #2 $51.71   12.443%   $58.1443   $58.14   $58.15   $58.10  
  Purchase #3 $186.48   7.564%   $200.5853   $200.59   $200.60   $200.60  
  Purchase #4 $250.79   13.770%   $285.3238   $285.32   $285.30   $285.30  
  Purchase #5 $47.40   6.795%   $50.6208   $50.62   $50.60   $50.60  
  Purchase #6 $153.75   5.296%   $161.8926   $161.89   $161.90   $161.90  
  6 purchase totals = $749.72       $823.5489   $823.54   $823.55   $823.50  
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?