Custom taxes are in the manager as of 3.3f, and this manager may be used
with earlier versions of agora that have the custom tax logic built-in
(version 3.1a and higher.)  If you'd like to try to use the newer manager
with the older version of agora, remember that any required settings under
your manager will need to be dealt with somehow!  If you use the newer
manager with these older versions keep in mind that the tax cannot be
switched "off" using the manager except by deleting the tax logic, or but
updating the logic in the agora_order_lib.pl file.

If you want a custom tax but do not want to use the updated manager, in
the agora.set.db file of versions up to 3.3c, at the top, enter lines like
these:

 $sc_extra_tax1_logic='(0.04)*$subtotal';
 $sc_extra_tax1_name='Philly Tax';

And it will calculate it for you.

You can have extra tax 1, 2, and 3 if you so desire.

In version 3.3d,e you can manage them manually in the
./admin_files/agora_user_lib.pl file.  Just setup your own section at the
bottom, calling it something like XCUSTOM_TAX, like this: 

#:#:#: start XCUSTOM_TAX settings
 $sc_extra_tax1_logic='(0.04)*$subtotal';
 $sc_extra_tax1_name='Philly Tax';
#:#:#: end XCUSTOM_TAX settings

It must come BELOW the normal TAX section, and the name you give it should
be named starting with an X for custom items (or ZX if there ever is a
manager settings section that comes after X and your code must go after
it).  Each time the agora_user_lib.pl file is updated by the manager
section names will be "upcased" and sorted in alphabetical order. 

On 3.3f and higher the custom taxes are available in the manager.
Remember you can use the custom tax logic for things other than tax.  For
example, if you want the "handling charge" to be specifically called that
in the totals table, then set the handling charge to zero and setup a
"custom tax" called "Handling Charge".  Be creative, and enjoy!