Green’s Dictionary of Slang

absolutely, completely.

2012		M. Lacher On the Bro’d 30: ‘I guess you only partied with him in the West.’ ‘Totes’.
2016		C. Eble (ed.) UNC-CH Campus Sl. Spring 2016 10: TOTES MY GOATS — < totes < totally + s expanded by nonsense rhyming .