When you create a report class, you can modify the scope you will be able to access from the report, by modifying self.localcontext.

You can, as below, add a binding to cr:

class my_report(report_sxw.rml_parse):

    def __init__(self, cr, uid, name, context):
        super(my_report, self).__init__(cr, uid, name, context=context)
        self.localcontext.update({'time': time,
                                  'cr': cr,
                                  'company_vat': self._get_company_vat})

    def _get_company_vat(self):
        res_users_obj = pooler.get_pool(self.cr.dbname).get('res.users')
        company_vat = res_users_obj.browse

In your report, you'll be able to use time, cr or company_vat().

You'll see that you can also add a binding for methods, this is maybe a better solution than directly access cr from your report.

On a side note, when you have some computation to do in a report, you often better have to compute it before the rendering of the template than during the rendering.

If you do not use a custom class and cannot create it (SaaS for example), you should be able to access to the current cursor with self._cr, if self is a browse_record.