From today, 16th September, the app should now display toll prices alongside any route using a toll road in the UK. If you are signed up for a TAG or Account for a local toll road / bridge then you can select the appropriate pass within the app and the toll prices should reflect the relevant discount, this also applies to the vehicle type you have chosen.
Passes and prices have no influence on routing, adding a pass for a toll will not make the routing servers prefer that route. You must still use the avoid tolls navigation setting in the app to be routed on non-toll routes. NB: This is with the exception of the London C Charge Exempt and London ULEZ Compliant as these passes do affect your routing in the central London area. More detail on dedicated forum thread.
You can see the list of mapped tolls in the UK Wazeopedia, and you will find any segment associated with a toll price now covered by a Map Comment and locked to L5, this is to prevent breaking the toll price function.

Please use this thread to report any errors you encounter with this feature, or if you know of a new toll route being opening, prices being changed, or even removed.

There are some minor toll roads that are yet to have their prices added, we hope to include these soon. The feature may also include inland ferry prices in the future.

EDIT: Currently this is restricted to Beta testers only.