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 $46.91   5.639%   $49.5553   $49.56   $49.55   $49.60  
  Purchase #2 $229.82   13.597%   $261.0686   $261.07   $261.05   $261.10  
  Purchase #3 $236.48   10.236%   $260.6861   $260.69   $260.70   $260.70  
  Purchase #4 $26.61   11.265%   $29.6076   $29.61   $29.60   $29.60  
  Purchase #5 $163.26   8.429%   $177.0212   $177.02   $177.00   $177.00  
  Purchase #6 $100.29   9.328%   $109.6451   $109.65   $109.65   $109.60  
  Purchase #7 $78.47   9.590%   $85.9953   $86.00   $86.00   $86.00  
  7 purchase totals = $881.84       $973.5792   $973.60   $973.55   $973.60