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 $250.28   4.573%   $261.7253   $261.73   $261.75   $261.70  
  Purchase #2 $152.35   4.654%   $159.4404   $159.44   $159.45   $159.40  
  Purchase #3 $183.55   6.392%   $195.2825   $195.28   $195.30   $195.30  
  Purchase #4 $109.26   4.440%   $114.1111   $114.11   $114.10   $114.10  
  Purchase #5 $185.28   8.197%   $200.4674   $200.47   $200.45   $200.50  
  Purchase #6 $47.38   4.692%   $49.6031   $49.60   $49.60   $49.60  
  Purchase #7 $24.95   13.309%   $28.2706   $28.27   $28.25   $28.30  
  7 purchase totals = $953.05       $1,008.9004   $1,008.90   $1,008.90   $1,008.90