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 $222.49   8.327%   $241.0167   $241.02   $241.00   $241.00  
  Purchase #2 $169.61   9.212%   $185.2345   $185.23   $185.25   $185.20  
  Purchase #3 $244.93   12.840%   $276.379   $276.38   $276.40   $276.40  
  Purchase #4 $228.44   12.543%   $257.0932   $257.09   $257.10   $257.10  
  Purchase #5 $90.33   9.152%   $98.597   $98.60   $98.60   $98.60  
  Purchase #6 $98.42   10.625%   $108.8771   $108.88   $108.90   $108.90  
  Purchase #7 $186.55   11.785%   $208.5349   $208.53   $208.55   $208.50  
  7 purchase totals = $1,240.77       $1,375.7324   $1,375.73   $1,375.80   $1,375.70