Well, for starters one would need to add an item to their store that is for this fee / tax. Avalara is actually already developing functionality so that on their backend they have a custom tax code for this fee. They're suggesting to their clients that they apply this tax code to a new product/sku that they create in their own systems with a $0.00 price. I'm assuming what's happening there is that on their back end it's applying the appropriate tax for that sku. If one doesn't use Avalara they'd probably just want to create a product/sku with that $.27 price.
To get it into the cart, I think one would have to develop a custom extension that includes a plugin that processes after the shipping address information is saved. Similar to here (https://magento.stackexchange.com/questions/182431/magento-2-how-to-get-an-event-after-shipping-addr...) but hooking in after (file for reference https://github.com/magento/magento2/blob/2.4-develop/app/code/Magento/Checkout/Model/ShippingInforma...). If this finds that the shipping address is to Colorado, check the cart for the above mentioned product, and if it is not there, add it (something like this https://meetanshi.com/blog/programmatically-add-product-to-cart-in-magento-2/).
To prevent them from being able to remove it one would have to update the template files for line items on the cart page and checkout page and include the product SKU/ID or some identifier as a class on the container for the line item (https://github.com/magento/magento2/blob/2.4-develop/app/code/Magento/Checkout/view/frontend/templat... and https://github.com/magento/magento2/blob/2.4-develop/app/code/Magento/Checkout/view/frontend/templat...). Then, using CSS or a conditional in the template itself, one would hide the buttons that allows users to remove that item from their cart.
As for preventing this from showing up for a customer that isn't required to pay sales tax, I'm not sure how that would be handled. I'm pretty sure for our client Avalara handles the tax exemptions, so I'm hoping that they'd recognize not to charge that tax in that case (even if the item is present in the cart). But, I'm not sure if Magento natively handles tax exemption as well in some way. If they do, and someone is using that, they'd want to check for this in the plugin I mentioned developing above that would be adding the line item to the cart.
This is just my guess. I'm not 100% sure if this would work out. But just based on the research I've been doing this is how I'd approach it.
