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 $248.49   5.252%   $261.5407   $261.54   $261.55   $261.50  
  Purchase #2 $184.51   11.252%   $205.2711   $205.27   $205.25   $205.30  
  Purchase #3 $71.93   13.868%   $81.9053   $81.91   $81.90   $81.90  
  Purchase #4 $223.39   12.756%   $251.8856   $251.89   $251.90   $251.90  
  Purchase #5 $54.77   5.241%   $57.6405   $57.64   $57.65   $57.60  
  Purchase #6 $246.85   7.620%   $265.66   $265.66   $265.65   $265.70  
  Purchase #7 $200.63   7.138%   $214.951   $214.95   $214.95   $215.00  
  7 purchase totals = $1,230.57       $1,338.8542   $1,338.86   $1,338.85   $1,338.90