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 $126.44   10.334%   $139.5063   $139.51   $139.50   $139.50  
  Purchase #2 $240.94   12.249%   $270.4527   $270.45   $270.45   $270.50  
  Purchase #3 $220.54   12.153%   $247.3422   $247.34   $247.35   $247.30  
  Purchase #4 $29.77   6.796%   $31.7932   $31.79   $31.80   $31.80  
  Purchase #5 $15.93   10.801%   $17.6506   $17.65   $17.65   $17.70  
  Purchase #6 $170.96   11.716%   $190.9897   $190.99   $191.00   $191.00  
  Purchase #7 $110.50   7.425%   $118.7046   $118.70   $118.70   $118.70  
  Purchase #8 $78.81   6.611%   $84.0201   $84.02   $84.00   $84.00  
  Purchase #9 $165.85   3.611%   $171.8388   $171.84   $171.85   $171.80  
  Purchase #10 $130.29   9.445%   $142.5959   $142.60   $142.60   $142.60  
  10 purchase totals = $1,290.03       $1,414.89   $1,414.90   $1,414.90  
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?