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 $227.81   13.688%   $258.9926   $258.99   $259.00   $259.00  
  Purchase #2 $185.87   5.147%   $195.4367   $195.44   $195.45   $195.40  
  Purchase #3 $126.55   5.301%   $133.2584   $133.26   $133.25   $133.30  
  Purchase #4 $194.81   8.698%   $211.7546   $211.75   $211.75   $211.80  
  Purchase #5 $98.86   11.167%   $109.8997   $109.90   $109.90   $109.90  
  Purchase #6 $158.82   13.191%   $179.7699   $179.77   $179.75   $179.80  
  Purchase #7 $166.59   4.687%   $174.3981   $174.40   $174.40   $174.40  
  Purchase #8 $218.56   12.783%   $246.4985   $246.50   $246.50   $246.50  
  Purchase #9 $49.58   5.610%   $52.3614   $52.36   $52.35   $52.40  
  Purchase #10 $164.29   9.455%   $179.8236   $179.82   $179.80   $179.80  
  10 purchase totals = $1,591.74       $1,742.1935   $1,742.19   $1,742.15   $1,742.30  
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?