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 $239.58   9.226%   $261.6837   $261.68   $261.70   $261.70  
  Purchase #2 $173.57   12.291%   $194.9035   $194.90   $194.90   $194.90  
  Purchase #3 $42.51   12.356%   $47.7625   $47.76   $47.75   $47.80  
  Purchase #4 $95.95   8.827%   $104.4195   $104.42   $104.40   $104.40  
  Purchase #5 $134.53   4.583%   $140.6955   $140.70   $140.70   $140.70  
  Purchase #6 $218.93   3.574%   $226.7546   $226.75   $226.75   $226.80  
  Purchase #7 $224.66   12.433%   $252.592   $252.59   $252.60   $252.60  
  7 purchase totals = $1,129.73       $1,228.8113   $1,228.80   $1,228.80   $1,228.90