Green’s Dictionary of Slang

absolutely, completely.

2014		C. Eble UNC-CH Campus Sl. Spring 2014 15: TOTES — totally + s totally : ‘We should totes get froyo after class.’ X: ‘That’s an awesome outfit.’ Y: ‘Totes.’.
2016		C. Eble (ed.) UNC-CH Campus Sl. Spring 2016 10: TOTES MY GOATS — < totes < totally + s expanded by nonsense rhyming .