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 $239.53   12.187%   $268.7215   $268.72   $268.70   $268.70  
  Purchase #2 $250.61   3.636%   $259.7222   $259.72   $259.70   $259.70  
  Purchase #3 $55.58   7.493%   $59.7446   $59.74   $59.75   $59.70  
  Purchase #4 $231.61   7.334%   $248.5963   $248.60   $248.60   $248.60  
  Purchase #5 $202.78   12.626%   $228.383   $228.38   $228.40   $228.40  
  Purchase #6 $168.33   3.602%   $174.3932   $174.39   $174.40   $174.40  
  Purchase #7 $168.97   10.119%   $186.0681   $186.07   $186.05   $186.10  
  7 purchase totals = $1,317.41       $1,425.6289   $1,425.62   $1,425.60   $1,425.60