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 $248.76   5.351%   $262.0711   $262.07   $262.05   $262.10  
  Purchase #2 $125.94   7.172%   $134.9724   $134.97   $134.95   $135.00  
  Purchase #3 $141.76   3.177%   $146.2637   $146.26   $146.25   $146.30  
  Purchase #4 $102.48   6.623%   $109.2673   $109.27   $109.25   $109.30  
  Purchase #5 $227.49   6.557%   $242.4065   $242.41   $242.40   $242.40  
  Purchase #6 $69.39   3.607%   $71.8929   $71.89   $71.90   $71.90  
  Purchase #7 $244.48   10.283%   $269.6199   $269.62   $269.60   $269.60  
  7 purchase totals = $1,160.30       $1,236.4938   $1,236.49   $1,236.40   $1,236.60