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 $211.57   7.407%   $227.241   $227.24   $227.25   $227.20  
  Purchase #2 $19.44   5.242%   $20.459   $20.46   $20.45   $20.50  
  Purchase #3 $45.55   12.189%   $51.1021   $51.10   $51.10   $51.10  
  Purchase #4 $82.80   11.289%   $92.1473   $92.15   $92.15   $92.10  
  Purchase #5 $245.94   6.271%   $261.3629   $261.36   $261.35   $261.40  
  Purchase #6 $8.53   11.789%   $9.5356   $9.54   $9.55   $9.50  
  Purchase #7 $189.31   5.786%   $200.2635   $200.26   $200.25   $200.30  
  7 purchase totals = $803.14       $862.1114   $862.11   $862.10   $862.10