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 $209.37   10.524%   $231.4041   $231.40   $231.40   $231.40  
  Purchase #2 $28.78   13.336%   $32.6181   $32.62   $32.60   $32.60  
  Purchase #3 $218.63   9.534%   $239.4742   $239.47   $239.45   $239.50  
  Purchase #4 $163.82   4.502%   $171.1952   $171.20   $171.20   $171.20  
  Purchase #5 $218.92   8.862%   $238.3207   $238.32   $238.30   $238.30  
  Purchase #6 $173.35   4.133%   $180.5146   $180.51   $180.50   $180.50  
  Purchase #7 $161.72   11.128%   $179.7162   $179.72   $179.70   $179.70  
  Purchase #8 $116.55   8.320%   $126.247   $126.25   $126.25   $126.20  
  Purchase #9 $132.28   7.767%   $142.5542   $142.55   $142.55   $142.60  
  Purchase #10 $118.62   4.341%   $123.7693   $123.77   $123.75   $123.80  
  10 purchase totals = $1,542.04       $1,665.81   $1,665.70   $1,665.80  
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?