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 $241.28   8.423%   $261.603   $261.60   $261.60   $261.60  
  Purchase #2 $121.51   5.361%   $128.0242   $128.02   $128.00   $128.00  
  Purchase #3 $238.30   4.622%   $249.3142   $249.31   $249.30   $249.30  
  Purchase #4 $170.81   4.509%   $178.5118   $178.51   $178.50   $178.50  
  Purchase #5 $8.68   6.699%   $9.2615   $9.26   $9.25   $9.30  
  Purchase #6 $187.32   10.329%   $206.6683   $206.67   $206.65   $206.70  
  Purchase #7 $30.50   13.537%   $34.6288   $34.63   $34.65   $34.60  
  7 purchase totals = $998.40       $1,068.0118   $1,068.00   $1,067.95   $1,068.00