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 $40.58   3.397%   $41.9585   $41.96   $41.95   $42.00  
  Purchase #2 $197.60   13.399%   $224.0764   $224.08   $224.10   $224.10  
  Purchase #3 $16.67   12.126%   $18.6914   $18.69   $18.70   $18.70  
  Purchase #4 $131.30   9.635%   $143.9508   $143.95   $143.95   $144.00  
  Purchase #5 $83.40   13.143%   $94.3613   $94.36   $94.35   $94.40  
  Purchase #6 $27.63   12.103%   $30.9741   $30.97   $30.95   $31.00  
  Purchase #7 $56.72   3.537%   $58.7262   $58.73   $58.75   $58.70  
  Purchase #8 $180.93   8.719%   $196.7053   $196.71   $196.70   $196.70  
  Purchase #9 $91.40   7.296%   $98.0685   $98.07   $98.05   $98.10  
  Purchase #10 $44.91   12.859%   $50.685   $50.69   $50.70   $50.70  
  10 purchase totals = $871.14       $958.1975   $958.21   $958.20   $958.40  
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?