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 $52.74   13.844%   $60.0413   $60.04   $60.05   $60.00  
  Purchase #2 $63.25   8.189%   $68.4295   $68.43   $68.45   $68.40  
  Purchase #3 $211.83   3.105%   $218.4073   $218.41   $218.40   $218.40  
  Purchase #4 $52.71   4.628%   $55.1494   $55.15   $55.15   $55.10  
  Purchase #5 $51.45   9.246%   $56.2071   $56.21   $56.20   $56.20  
  Purchase #6 $111.66   4.230%   $116.3832   $116.38   $116.40   $116.40  
  Purchase #7 $157.68   10.831%   $174.7583   $174.76   $174.75   $174.80  
  7 purchase totals = $701.32       $749.3761   $749.38   $749.40   $749.30