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 $112.76   5.126%   $118.5401   $118.54   $118.55   $118.50  
  Purchase #2 $59.29   7.691%   $63.85   $63.85   $63.85   $63.90  
  Purchase #3 $76.76   8.855%   $83.5571   $83.56   $83.55   $83.60  
  Purchase #4 $235.80   10.800%   $261.2664   $261.27   $261.25   $261.30  
  Purchase #5 $35.81   12.699%   $40.3575   $40.36   $40.35   $40.40  
  Purchase #6 $81.41   7.808%   $87.7665   $87.77   $87.75   $87.80  
  Purchase #7 $232.32   5.504%   $245.1069   $245.11   $245.10   $245.10  
  7 purchase totals = $834.15       $900.4445   $900.46   $900.40   $900.60