Let's do some math ..  Rounding examples of 6 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $250.75   4.281%   $261.4846   $261.48   $261.50   $261.50  
  Purchase #2 $195.35   4.395%   $203.9356   $203.94   $203.95   $203.90  
  Purchase #3 $156.52   10.121%   $172.3614   $172.36   $172.35   $172.40  
  Purchase #4 $227.28   5.675%   $240.1781   $240.18   $240.20   $240.20  
  Purchase #5 $52.95   6.747%   $56.5225   $56.52   $56.50   $56.50  
  Purchase #6 $114.80   13.635%   $130.453   $130.45   $130.45   $130.50  
  6 purchase totals = $997.65       $1,064.93   $1,064.95   $1,065.00  
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?