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 $44.38   9.154%   $48.4425   $48.44   $48.45   $48.40  
  Purchase #2 $157.69   7.621%   $169.7076   $169.71   $169.70   $169.70  
  Purchase #3 $155.97   4.268%   $162.6268   $162.63   $162.65   $162.60  
  Purchase #4 $88.55   11.126%   $98.4021   $98.40   $98.40   $98.40  
  Purchase #5 $118.76   11.873%   $132.8604   $132.86   $132.85   $132.90  
  Purchase #6 $231.53   10.323%   $255.4308   $255.43   $255.45   $255.40  
  Purchase #7 $47.67   5.103%   $50.1026   $50.10   $50.10   $50.10  
  7 purchase totals = $844.55       $917.5728   $917.57   $917.60   $917.50