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 $139.76   4.428%   $145.9486   $145.95   $145.95   $145.90  
  Purchase #2 $198.71   4.708%   $208.0653   $208.07   $208.05   $208.10  
  Purchase #3 $31.29   5.381%   $32.9737   $32.97   $32.95   $33.00  
  Purchase #4 $126.62   3.671%   $131.2682   $131.27   $131.25   $131.30  
  Purchase #5 $173.32   4.180%   $180.5648   $180.56   $180.55   $180.60  
  Purchase #6 $248.45   8.515%   $269.6055   $269.61   $269.60   $269.60  
  Purchase #7 $174.44   5.287%   $183.6626   $183.66   $183.65   $183.70  
  Purchase #8 $46.39   12.411%   $52.1475   $52.15   $52.15   $52.10  
  Purchase #9 $225.92   13.490%   $256.3966   $256.40   $256.40   $256.40  
  Purchase #10 $219.48   11.589%   $244.9155   $244.92   $244.90   $244.90  
  10 purchase totals = $1,584.38       $1,705.5483   $1,705.56   $1,705.45   $1,705.60  
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?