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 $248.55   5.249%   $261.5964   $261.60   $261.60   $261.60  
  Purchase #2 $177.53   3.563%   $183.8554   $183.86   $183.85   $183.90  
  Purchase #3 $6.38   7.127%   $6.8347   $6.83   $6.85   $6.80  
  Purchase #4 $226.54   6.716%   $241.7544   $241.75   $241.75   $241.80  
  Purchase #5 $47.72   12.202%   $53.5428   $53.54   $53.55   $53.50  
  Purchase #6 $51.57   6.283%   $54.8101   $54.81   $54.80   $54.80  
  Purchase #7 $164.88   10.295%   $181.8544   $181.85   $181.85   $181.90  
  7 purchase totals = $923.17       $984.2482   $984.24   $984.25   $984.30