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 $179.92   13.572%   $204.3387   $204.34   $204.35   $204.30  
  Purchase #2 $173.30   7.730%   $186.6961   $186.70   $186.70   $186.70  
  Purchase #3 $45.63   12.264%   $51.2261   $51.23   $51.25   $51.20  
  Purchase #4 $226.43   4.737%   $237.156   $237.16   $237.15   $237.20  
  Purchase #5 $100.99   3.624%   $104.6499   $104.65   $104.65   $104.60  
  Purchase #6 $166.73   5.262%   $175.5033   $175.50   $175.50   $175.50  
  Purchase #7 $42.87   12.540%   $48.2459   $48.25   $48.25   $48.20  
  7 purchase totals = $935.87       $1,007.8160   $1,007.83   $1,007.85   $1,007.70