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 $216.54   3.825%   $224.8227   $224.82   $224.80   $224.80  
  Purchase #2 $92.42   7.734%   $99.5678   $99.57   $99.55   $99.60  
  Purchase #3 $96.49   13.443%   $109.4612   $109.46   $109.45   $109.50  
  Purchase #4 $171.92   10.254%   $189.5487   $189.55   $189.55   $189.50  
  Purchase #5 $152.38   12.142%   $170.882   $170.88   $170.90   $170.90  
  Purchase #6 $111.70   8.579%   $121.2827   $121.28   $121.30   $121.30  
  Purchase #7 $123.26   5.784%   $130.3894   $130.39   $130.40   $130.40  
  Purchase #8 $235.54   7.521%   $253.255   $253.26   $253.25   $253.30  
  Purchase #9 $124.62   12.807%   $140.5801   $140.58   $140.60   $140.60  
  Purchase #10 $100.93   12.784%   $113.8329   $113.83   $113.85   $113.80  
  10 purchase totals = $1,425.80       $1,553.62   $1,553.65   $1,553.70  
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?