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 $209.92   11.329%   $233.7018   $233.70   $233.70   $233.70  
  Purchase #2 $119.90   10.617%   $132.6298   $132.63   $132.65   $132.60  
  Purchase #3 $236.31   10.405%   $260.8981   $260.90   $260.90   $260.90  
  Purchase #4 $242.72   7.631%   $261.242   $261.24   $261.25   $261.20  
  Purchase #5 $77.56   8.182%   $83.906   $83.91   $83.90   $83.90  
  Purchase #6 $53.70   12.587%   $60.4592   $60.46   $60.45   $60.50  
  Purchase #7 $77.60   12.208%   $87.0734   $87.07   $87.05   $87.10  
  7 purchase totals = $1,017.71       $1,119.9103   $1,119.91   $1,119.90   $1,119.90