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 $57.83   9.729%   $63.4563   $63.46   $63.45   $63.50  
  Purchase #2 $146.70   7.313%   $157.4282   $157.43   $157.45   $157.40  
  Purchase #3 $153.46   4.646%   $160.5898   $160.59   $160.60   $160.60  
  Purchase #4 $114.36   4.413%   $119.4067   $119.41   $119.40   $119.40  
  Purchase #5 $32.99   6.851%   $35.2501   $35.25   $35.25   $35.30  
  Purchase #6 $226.73   8.569%   $246.1585   $246.16   $246.15   $246.20  
  Purchase #7 $226.30   6.183%   $240.2921   $240.29   $240.30   $240.30  
  7 purchase totals = $958.37       $1,022.5817   $1,022.59   $1,022.60   $1,022.70