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 $44.42   11.498%   $49.5274   $49.53   $49.55   $49.50  
  Purchase #2 $32.53   10.642%   $35.9918   $35.99   $36.00   $36.00  
  Purchase #3 $40.96   3.396%   $42.351   $42.35   $42.35   $42.40  
  Purchase #4 $22.85   13.858%   $26.0166   $26.02   $26.00   $26.00  
  Purchase #5 $223.45   13.340%   $253.2582   $253.26   $253.25   $253.30  
  Purchase #6 $141.31   12.856%   $159.4768   $159.48   $159.50   $159.50  
  Purchase #7 $135.67   6.568%   $144.5808   $144.58   $144.60   $144.60  
  Purchase #8 $83.85   5.286%   $88.2823   $88.28   $88.30   $88.30  
  Purchase #9 $237.42   8.491%   $257.5793   $257.58   $257.60   $257.60  
  Purchase #10 $217.76   8.842%   $237.0143   $237.01   $237.00   $237.00  
  10 purchase totals = $1,180.22       $1,294.0785   $1,294.08   $1,294.15   $1,294.20  
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?