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 $245.45   6.699%   $261.8927   $261.89   $261.90   $261.90  
  Purchase #2 $115.69   7.187%   $124.0046   $124.00   $124.00   $124.00  
  Purchase #3 $238.70   6.608%   $254.4733   $254.47   $254.45   $254.50  
  Purchase #4 $42.48   12.255%   $47.6859   $47.69   $47.70   $47.70  
  Purchase #5 $102.92   6.275%   $109.3782   $109.38   $109.40   $109.40  
  Purchase #6 $236.76   4.195%   $246.6921   $246.69   $246.70   $246.70  
  Purchase #7 $151.37   6.649%   $161.4346   $161.43   $161.45   $161.40  
  7 purchase totals = $1,133.37       $1,205.5614   $1,205.55   $1,205.60   $1,205.60