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 $132.26   10.265%   $145.8365   $145.84   $145.85   $145.80  
  Purchase #2 $55.53   12.181%   $62.2941   $62.29   $62.30   $62.30  
  Purchase #3 $30.79   8.386%   $33.372   $33.37   $33.35   $33.40  
  Purchase #4 $198.67   3.246%   $205.1188   $205.12   $205.10   $205.10  
  Purchase #5 $13.42   3.438%   $13.8814   $13.88   $13.90   $13.90  
  Purchase #6 $85.46   11.523%   $95.3076   $95.31   $95.30   $95.30  
  Purchase #7 $137.41   12.245%   $154.2359   $154.24   $154.25   $154.20  
  Purchase #8 $248.53   3.320%   $256.7812   $256.78   $256.80   $256.80  
  Purchase #9 $171.35   7.411%   $184.0487   $184.05   $184.05   $184.00  
  Purchase #10 $157.83   6.421%   $167.9643   $167.96   $167.95   $168.00  
  10 purchase totals = $1,231.25       $1,318.84   $1,318.85   $1,318.80  
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?