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 $245.76   6.292%   $261.2232   $261.22   $261.20   $261.20  
  Purchase #2 $169.81   11.475%   $189.2957   $189.30   $189.30   $189.30  
  Purchase #3 $205.58   4.526%   $214.8846   $214.88   $214.90   $214.90  
  Purchase #4 $227.91   4.206%   $237.4959   $237.50   $237.50   $237.50  
  Purchase #5 $77.46   3.641%   $80.2803   $80.28   $80.30   $80.30  
  Purchase #6 $200.90   10.290%   $221.5726   $221.57   $221.55   $221.60  
  Purchase #7 $180.52   5.631%   $190.6851   $190.69   $190.70   $190.70  
  7 purchase totals = $1,307.94       $1,395.4374   $1,395.44   $1,395.45   $1,395.50