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 $169.36   13.441%   $192.1237   $192.12   $192.10   $192.10  
  Purchase #2 $35.74   10.636%   $39.5413   $39.54   $39.55   $39.50  
  Purchase #3 $249.43   6.528%   $265.7128   $265.71   $265.70   $265.70  
  Purchase #4 $132.49   5.607%   $139.9187   $139.92   $139.90   $139.90  
  Purchase #5 $215.70   3.309%   $222.8375   $222.84   $222.85   $222.80  
  Purchase #6 $170.51   4.163%   $177.6083   $177.61   $177.60   $177.60  
  Purchase #7 $159.40   13.221%   $180.4743   $180.47   $180.45   $180.50  
  Purchase #8 $198.57   10.674%   $219.7654   $219.77   $219.75   $219.80  
  Purchase #9 $107.90   6.156%   $114.5423   $114.54   $114.55   $114.50  
  Purchase #10 $159.38   3.443%   $164.8675   $164.87   $164.85   $164.90  
  10 purchase totals = $1,598.48       $1,717.39   $1,717.30   $1,717.30  
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?