Add a field in `admin > system > configuration Sales`

Question

How can I add a field in admin panel > system > configuration > Sales ?

Answer 1

You can add the new group in sales with following code.

Add it to your modules system.xml file.

<config>
    <sections>
         <sales>
            <groups>
                <newgroup translate="label" module="sales">
                    <label>New</label>
                    <frontend_type>text</frontend_type>
                    <sort_order>250</sort_order>
                    <show_in_default>1</show_in_default>
                    <show_in_website>1</show_in_website>
                    <show_in_store>1</show_in_store>
                    <fields>
                        <new_field translate="label">
                            <label>New</label>
                            <frontend_type>select</frontend_type>
                            <source_model>adminhtml/system_config_source_yesno</source_model>
                            <sort_order>1</sort_order>
                            <show_in_default>1</show_in_default>
                            <show_in_website>1</show_in_website>
                            <show_in_store>1</show_in_store>
                        </new_field>
                    </fields>
                </newgroup>
            </groups>
        </sales>
    </sections>
</config> 

You can add a field in already existing group

<config>
    <sections>
         <sales>
            <groups>
                <general>
                    <fields>
                        <new_field_ex_group translate="label">
                            <label>New Ex Group</label>
                            <frontend_type>select</frontend_type>
                            <source_model>adminhtml/system_config_source_yesno</source_model>
                            <sort_order>1</sort_order>
                            <show_in_default>1</show_in_default>
                            <show_in_website>1</show_in_website>
                            <show_in_store>1</show_in_store>
                        </new_field_ex_group>
                    </fields>
                </general>
            </groups>
        </sales>
    </sections>
</config>

Refer Link

Edit :

To add new tab in sales section

<config>
    <sections>
        <yoursection translate="label">
            <label>Your section under sales</label>
            <tab>sales</tab> <!-- you can change to any deafult tabs -->
            <frontend_type>text</frontend_type>
            <sort_order>500</sort_order>
            <show_in_default>1</show_in_default>
            <show_in_website>1</show_in_website>
            <show_in_store>1</show_in_store>
        </yoursection>
    </sections>
</config>