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 $103.83   10.452%   $114.6823   $114.68   $114.70   $114.70  
  Purchase #2 $231.77   7.544%   $249.2547   $249.25   $249.25   $249.30  
  Purchase #3 $205.96   7.713%   $221.8457   $221.85   $221.85   $221.80  
  Purchase #4 $249.62   4.719%   $261.3996   $261.40   $261.40   $261.40  
  Purchase #5 $156.92   8.707%   $170.583   $170.58   $170.60   $170.60  
  Purchase #6 $69.83   5.717%   $73.8222   $73.82   $73.80   $73.80  
  Purchase #7 $165.62   12.229%   $185.8737   $185.87   $185.85   $185.90  
  7 purchase totals = $1,183.55       $1,277.4612   $1,277.45   $1,277.45   $1,277.50