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 $186.30   5.845%   $197.1892   $197.19   $197.20   $197.20  
  Purchase #2 $218.46   6.683%   $233.0597   $233.06   $233.05   $233.10  
  Purchase #3 $250.88   11.467%   $279.6484   $279.65   $279.65   $279.60  
  Purchase #4 $167.34   11.115%   $185.9398   $185.94   $185.95   $185.90  
  Purchase #5 $92.27   10.672%   $102.1171   $102.12   $102.10   $102.10  
  Purchase #6 $108.25   12.475%   $121.7542   $121.75   $121.75   $121.80  
  Purchase #7 $33.28   12.452%   $37.424   $37.42   $37.40   $37.40  
  Purchase #8 $231.43   11.872%   $258.9054   $258.91   $258.90   $258.90  
  Purchase #9 $246.49   7.580%   $265.1739   $265.17   $265.15   $265.20  
  Purchase #10 $97.57   11.330%   $108.6247   $108.62   $108.60   $108.60  
  10 purchase totals = $1,632.27       $1,789.8364   $1,789.83   $1,789.75   $1,789.80  
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?