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 $218.81   10.113%   $240.9383   $240.94   $240.95   $240.90  
  Purchase #2 $235.68   10.711%   $260.9237   $260.92   $260.90   $260.90  
  Purchase #3 $79.81   3.492%   $82.597   $82.60   $82.60   $82.60  
  Purchase #4 $17.31   13.575%   $19.6598   $19.66   $19.65   $19.70  
  Purchase #5 $46.85   13.460%   $53.156   $53.16   $53.15   $53.20  
  Purchase #6 $45.63   3.602%   $47.2736   $47.27   $47.25   $47.30  
  Purchase #7 $55.73   9.286%   $60.9051   $60.91   $60.90   $60.90  
  7 purchase totals = $699.82       $765.4535   $765.46   $765.40   $765.50