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 $177.57   8.796%   $193.1891   $193.19   $193.20   $193.20  
  Purchase #2 $139.75   10.649%   $154.632   $154.63   $154.65   $154.60  
  Purchase #3 $98.69   4.565%   $103.1952   $103.20   $103.20   $103.20  
  Purchase #4 $239.65   3.272%   $247.4913   $247.49   $247.50   $247.50  
  Purchase #5 $48.42   4.803%   $50.7456   $50.75   $50.75   $50.70  
  Purchase #6 $131.66   6.622%   $140.3785   $140.38   $140.40   $140.40  
  Purchase #7 $247.92   11.593%   $276.6614   $276.66   $276.65   $276.70  
  7 purchase totals = $1,083.66       $1,166.2931   $1,166.30   $1,166.35   $1,166.30