XUMM focusses at receiving/sending XRP (1 XRP = 1 XRP) and sending/receiving fiat currencies in IOU's (eg. Bitstamp issued USD / Gatehub issued EUR, etc.) Of course the IOU's will represent their fiat value.
To view your main XRP balance in fiat equivalent, simply tap the XRP balance on the home screen. To see the value for all your individual tokens held, open the 'Account Worth' xApp: