It says 0.1 Ohms when switching 6 volts. That may be "worst case" at a voltage too low to wet the contacts, or an initial figure.
Any decent high current relay should have a contact resistance little more than that of the total metal path through it, a few milliohms at most.
Just looking at the data for a 10A Omron relay we use a lot, that also says 100 mOhm - but there is a footnote to the table saying the data is "Initial values" so I'd say that is after storage and before they have had an adequate wetting voltage applied in use.