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 $86.87   13.516%   $98.6113   $98.61   $98.60   $98.60  
  Purchase #2 $182.95   5.731%   $193.4349   $193.43   $193.45   $193.40  
  Purchase #3 $19.81   13.335%   $22.4517   $22.45   $22.45   $22.50  
  Purchase #4 $163.48   11.563%   $182.3832   $182.38   $182.40   $182.40  
  Purchase #5 $240.38   10.619%   $265.906   $265.91   $265.90   $265.90  
  Purchase #6 $86.89   13.620%   $98.7244   $98.72   $98.70   $98.70  
  Purchase #7 $18.54   10.682%   $20.5204   $20.52   $20.50   $20.50  
  7 purchase totals = $798.92       $882.0319   $882.02   $882.00   $882.00