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 $190.75   13.676%   $216.837   $216.84   $216.85   $216.80  
  Purchase #2 $105.82   8.242%   $114.5417   $114.54   $114.55   $114.50  
  Purchase #3 $217.92   4.291%   $227.2709   $227.27   $227.25   $227.30  
  Purchase #4 $241.48   5.826%   $255.5486   $255.55   $255.55   $255.50  
  Purchase #5 $132.63   3.121%   $136.7694   $136.77   $136.75   $136.80  
  Purchase #6 $203.33   8.423%   $220.4565   $220.46   $220.45   $220.50  
  Purchase #7 $190.91   4.742%   $199.963   $199.96   $199.95   $200.00  
  7 purchase totals = $1,282.84       $1,371.3871   $1,371.39   $1,371.35   $1,371.40