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 $9.65   7.622%   $10.3855   $10.39   $10.40   $10.40  
  Purchase #2 $186.39   7.685%   $200.7141   $200.71   $200.70   $200.70  
  Purchase #3 $97.99   10.563%   $108.3407   $108.34   $108.35   $108.30  
  Purchase #4 $166.99   11.815%   $186.7199   $186.72   $186.70   $186.70  
  Purchase #5 $18.87   8.434%   $20.4615   $20.46   $20.45   $20.50  
  Purchase #6 $163.75   8.178%   $177.1415   $177.14   $177.15   $177.10  
  Purchase #7 $30.69   10.352%   $33.867   $33.87   $33.85   $33.90  
  7 purchase totals = $674.33       $737.6302   $737.63   $737.60   $737.60