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 $186.37   11.655%   $208.0914   $208.09   $208.10   $208.10  
  Purchase #2 $246.49   12.318%   $276.8526   $276.85   $276.85   $276.90  
  Purchase #3 $53.87   12.456%   $60.58   $60.58   $60.60   $60.60  
  Purchase #4 $222.32   12.361%   $249.801   $249.80   $249.80   $249.80  
  Purchase #5 $85.42   12.119%   $95.772   $95.77   $95.75   $95.80  
  Purchase #6 $234.40   11.412%   $261.1497   $261.15   $261.15   $261.10  
  Purchase #7 $77.85   11.507%   $86.8082   $86.81   $86.80   $86.80  
  7 purchase totals = $1,106.72       $1,239.0549   $1,239.05   $1,239.05   $1,239.10