Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $167.38   9.324%   $182.9865   $182.99   $183.00   $183.00  
  Purchase #2 $146.30   7.252%   $156.9097   $156.91   $156.90   $156.90  
  Purchase #3 $221.95   13.771%   $252.5147   $252.51   $252.50   $252.50  
  Purchase #4 $93.40   4.623%   $97.7179   $97.72   $97.70   $97.70  
  Purchase #5 $41.68   13.222%   $47.1909   $47.19   $47.20   $47.20  
  Purchase #6 $59.66   7.622%   $64.2073   $64.21   $64.20   $64.20  
  Purchase #7 $24.84   4.676%   $26.0015   $26.00   $26.00   $26.00  
  7 purchase totals = $755.21       $827.5285   $827.53   $827.50   $827.50