Is this your first time registering your vehicle?
Yes
In that case you have to pay both the registration and vehicle plate fees
Does the online estimate include sales tax?
No
Where can I find information on trailer registrations?
Trailer and boat registration fees are calculated differently. You can t use the online service to estimate them. See register a trailer, or register a boat for how to estimate these registration fees
What are the estimate fees online?
The online estimates DOES NOT include the sales tax
Can I use these estimates for commercial vehicles?
I do see the chart but it does not make sense to me.  Could you please explain the columns in this chart to me?
The chart shows you a list of counties: find the one you are living in and see the amount of the use tax.You also have one chart for the registration fee depending on how much your vehicle weights.
Yes for both passenger and commercial.
I'd like to ask regarding the estimate fees and taxes. Can I use the online service to estimate fees and taxes for a trailer?