Diagnose a WooCommerce tax calculation issue for multi-region selling

A WooCommerce store selling in both the US and Canada has reported tax amounts that
look wrong on some orders. Details:

STORE BASE: [Austin, Texas]
SELLING TO: [all US states plus Canada]
RECENT CHANGE: [store crossed the economic nexus threshold in a new state, Colorado,
last month and started collecting there]
SYMPTOM: [some Texas orders are being taxed at what looks like a different rate than
expected, and some Canadian orders show no GST/HST at all]
CART DETAIL: [a handful of affected orders mix a physical product with a digital
download, like an e-book care guide bundled with a physical item]

Walk through the diagnosis in this order:

1. Confirm the store's tax setting for origin-based vs destination-based calculation
   matches what Texas (and each relevant state) actually requires, since Texas is
   origin-based for in-state sales but destination-based rules apply for many other
   states, and a store-wide setting that assumes one model everywhere will misprice
   tax specifically on the states that don't follow that model.
2. Check whether the new Colorado nexus was actually added as a tax rate row (WooCommerce
   doesn't automatically detect new nexus, it has to be manually configured or synced via
   a tax plugin), since crossing an economic threshold doesn't create the rate itself, a
   missing rate row for Colorado would show as $0 tax collected there, not an error.
3. Check whether affected products have the correct tax class assigned (standard vs a
   reduced or zero rate class), since a product accidentally left in a "zero rate" tax
   class from a prior promotion or import would show $0 tax regardless of correct nexus
   configuration, which matches the Canadian GST/HST-missing symptom if those specific
   products are misclassified rather than an actual nexus or rate-table problem.
4. For the mixed digital-plus-physical cart, confirm the digital download has its own
   correct tax class, since digital goods are taxed differently from physical goods in
   several jurisdictions (including some Canadian provinces), and a single tax class
   applied to the whole order rather than calculated per line item would produce a
   total that's wrong in either direction depending on which rate got applied to both
   items.
5. As a last check, verify rounding: WooCommerce can calculate tax per line item or on
   the cart subtotal depending on a setting, and a mismatch here produces small
   penny-level discrepancies that look like "wrong tax" reports from careful customers
   even when the underlying rate is correct.

Replace the bracketed base location, new nexus state, and symptom details with your
own store's actual situation.