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 $35.26   3.553%   $36.5128   $36.51   $36.50   $36.50  
  Purchase #2 $179.65   5.543%   $189.608   $189.61   $189.60   $189.60  
  Purchase #3 $44.58   11.865%   $49.8694   $49.87   $49.85   $49.90  
  Purchase #4 $20.93   12.429%   $23.5314   $23.53   $23.55   $23.50  
  Purchase #5 $126.87   5.565%   $133.9303   $133.93   $133.95   $133.90  
  Purchase #6 $235.93   4.208%   $245.8579   $245.86   $245.85   $245.90  
  Purchase #7 $176.49   10.275%   $194.6243   $194.62   $194.60   $194.60  
  Purchase #8 $183.56   7.571%   $197.4573   $197.46   $197.45   $197.50  
  Purchase #9 $122.92   9.679%   $134.8174   $134.82   $134.80   $134.80  
  Purchase #10 $209.93   13.143%   $237.5211   $237.52   $237.50   $237.50  
  10 purchase totals = $1,336.12       $1,443.7299   $1,443.73   $1,443.65   $1,443.70  
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?