Magento 1 : Adding currency to system configuration in Magento

If you want to add currency to your system configuration in Magento admin then you need to add the following code to your system.xml

Single select configuraton

<config>
  <sections>
    .......
    <fields>
     <base_currency translate="label">
      <label>Base Currency</label>
      <frontend_type>select</frontend_type>
      <source_model>adminhtml/system_config_source_currency</source_model>
      <sort_order>10</sort_order>
      <show_in_default>1</show_in_default>
      <show_in_website>1</show_in_website>
      <show_in_store>1</show_in_store>
     </base_currency>
    </fields>
    ........
  </sections>
</config>

Multi select configuration

<config>
  <sections>
    .......
    <fields>
     <base_currency translate="label">
      <label>Base Currency</label>
      <frontend_type>multiselect</frontend_type>
      <source_model>adminhtml/system_config_source_currency</source_model>
      <sort_order>10</sort_order>
      <show_in_default>1</show_in_default>
      <show_in_website>1</show_in_website>
      <show_in_store>1</show_in_store>
     </base_currency>
    </fields>
    ........
  </sections>
</config>