In your python file define field.

currency_id=fields.Many2one('res.currency', 'Currency', required=True)

in your xml file.

<field name="basic_pay" style="width:60%%" widget="monetary" options="{'currency_field': 'currency_id'}"/>

<field name="currency_id" ref="base.USD"/>

here i use basic salary with usd symbol.

We have created the currency changing facility for loged in users.

For,this user must be a registerd and login.

When user select the currency in website's header, set the pricelist created for that currency in to partner related to loged in user.

You can achive this using json call from the javascript.