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 $206.45   5.383%   $217.5632   $217.56   $217.55   $217.60  
  Purchase #2 $124.32   12.813%   $140.2491   $140.25   $140.25   $140.20  
  Purchase #3 $44.37   13.379%   $50.3063   $50.31   $50.30   $50.30  
  Purchase #4 $242.61   7.837%   $261.6233   $261.62   $261.60   $261.60  
  Purchase #5 $129.76   3.557%   $134.3756   $134.38   $134.40   $134.40  
  Purchase #6 $176.51   8.568%   $191.6334   $191.63   $191.65   $191.60  
  Purchase #7 $21.56   8.108%   $23.3081   $23.31   $23.30   $23.30  
  7 purchase totals = $945.58       $1,019.0590   $1,019.06   $1,019.05   $1,019.00