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 $182.73   4.807%   $191.5138   $191.51   $191.50   $191.50  
  Purchase #2 $238.49   5.843%   $252.425   $252.43   $252.45   $252.40  
  Purchase #3 $32.48   11.609%   $36.2506   $36.25   $36.25   $36.30  
  Purchase #4 $5.82   5.275%   $6.127   $6.13   $6.15   $6.10  
  Purchase #5 $41.44   8.455%   $44.9438   $44.94   $44.95   $44.90  
  Purchase #6 $142.81   4.127%   $148.7038   $148.70   $148.70   $148.70  
  Purchase #7 $232.36   7.161%   $248.9993   $249.00   $249.00   $249.00  
  Purchase #8 $66.59   4.451%   $69.5539   $69.55   $69.55   $69.60  
  Purchase #9 $8.34   12.787%   $9.4064   $9.41   $9.40   $9.40  
  Purchase #10 $99.76   13.240%   $112.9682   $112.97   $112.95   $113.00  
  10 purchase totals = $1,050.82       $1,120.89   $1,120.90   $1,120.90  
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?