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 $168.92   8.517%   $183.3069   $183.31   $183.30   $183.30  
  Purchase #2 $233.55   3.133%   $240.8671   $240.87   $240.85   $240.90  
  Purchase #3 $33.52   13.343%   $37.9926   $37.99   $38.00   $38.00  
  Purchase #4 $62.30   10.114%   $68.601   $68.60   $68.60   $68.60  
  Purchase #5 $201.89   11.533%   $225.174   $225.17   $225.15   $225.20  
  Purchase #6 $118.59   3.281%   $122.4809   $122.48   $122.50   $122.50  
  Purchase #7 $97.65   9.676%   $107.0986   $107.10   $107.10   $107.10  
  Purchase #8 $44.65   3.413%   $46.1739   $46.17   $46.15   $46.20  
  Purchase #9 $71.85   10.123%   $79.1234   $79.12   $79.10   $79.10  
  Purchase #10 $107.31   3.340%   $110.8942   $110.89   $110.90   $110.90  
  10 purchase totals = $1,140.23       $1,221.7126   $1,221.70   $1,221.65   $1,221.80  
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?