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 $235.37   10.176%   $259.3213   $259.32   $259.30   $259.30  
  Purchase #2 $97.46   5.335%   $102.6595   $102.66   $102.65   $102.70  
  Purchase #3 $21.50   5.471%   $22.6763   $22.68   $22.70   $22.70  
  Purchase #4 $213.89   5.767%   $226.225   $226.23   $226.25   $226.20  
  Purchase #5 $68.63   5.600%   $72.4733   $72.47   $72.45   $72.50  
  Purchase #6 $31.74   12.164%   $35.6009   $35.60   $35.60   $35.60  
  Purchase #7 $145.57   12.462%   $163.7109   $163.71   $163.70   $163.70  
  7 purchase totals = $814.16       $882.6672   $882.67   $882.65   $882.70