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 $240.34   12.291%   $269.8802   $269.88   $269.90   $269.90  
  Purchase #2 $176.79   3.302%   $182.6276   $182.63   $182.65   $182.60  
  Purchase #3 $44.66   12.507%   $50.2456   $50.25   $50.25   $50.20  
  Purchase #4 $86.68   13.546%   $98.4217   $98.42   $98.40   $98.40  
  Purchase #5 $116.61   13.786%   $132.6859   $132.69   $132.70   $132.70  
  Purchase #6 $104.51   10.870%   $115.8702   $115.87   $115.85   $115.90  
  Purchase #7 $173.49   9.663%   $190.2543   $190.25   $190.25   $190.30  
  7 purchase totals = $943.08       $1,039.9855   $1,039.99   $1,040.00   $1,040.00