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 $224.95   10.552%   $248.6867   $248.69   $248.70   $248.70  
  Purchase #2 $32.48   8.357%   $35.1944   $35.19   $35.20   $35.20  
  Purchase #3 $223.44   5.681%   $236.1336   $236.13   $236.15   $236.10  
  Purchase #4 $35.66   7.283%   $38.2571   $38.26   $38.25   $38.30  
  Purchase #5 $46.33   9.737%   $50.8412   $50.84   $50.85   $50.80  
  Purchase #6 $207.43   12.236%   $232.8111   $232.81   $232.80   $232.80  
  Purchase #7 $237.63   10.170%   $261.797   $261.80   $261.80   $261.80  
  7 purchase totals = $1,007.92       $1,103.7211   $1,103.72   $1,103.75   $1,103.70