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 $55.47   13.336%   $62.8675   $62.87   $62.85   $62.90  
  Purchase #2 $131.75   6.850%   $140.7749   $140.77   $140.75   $140.80  
  Purchase #3 $159.82   13.114%   $180.7788   $180.78   $180.80   $180.80  
  Purchase #4 $154.93   10.191%   $170.7189   $170.72   $170.70   $170.70  
  Purchase #5 $185.71   6.281%   $197.3744   $197.37   $197.35   $197.40  
  Purchase #6 $196.80   9.517%   $215.5295   $215.53   $215.55   $215.50  
  Purchase #7 $69.28   7.551%   $74.5113   $74.51   $74.50   $74.50  
  Purchase #8 $130.54   9.316%   $142.7011   $142.70   $142.70   $142.70  
  Purchase #9 $39.48   6.743%   $42.1421   $42.14   $42.15   $42.10  
  Purchase #10 $85.53   5.538%   $90.2667   $90.27   $90.25   $90.30  
  10 purchase totals = $1,209.31       $1,317.6652   $1,317.66   $1,317.60   $1,317.70  
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?