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 $86.71   13.526%   $98.4384   $98.44   $98.45   $98.40  
  Purchase #2 $223.57   9.804%   $245.4888   $245.49   $245.50   $245.50  
  Purchase #3 $151.95   3.277%   $156.9294   $156.93   $156.95   $156.90  
  Purchase #4 $114.81   13.766%   $130.6147   $130.61   $130.60   $130.60  
  Purchase #5 $128.47   5.400%   $135.4074   $135.41   $135.40   $135.40  
  Purchase #6 $30.63   9.260%   $33.4663   $33.47   $33.45   $33.50  
  Purchase #7 $159.79   13.707%   $181.6924   $181.69   $181.70   $181.70  
  7 purchase totals = $895.93       $982.0374   $982.04   $982.05   $982.00