Tax rates
Under Payments → Settings → Tax Rates. Set up the rates you charge once and apply them where they belong.
Adding one
Add tax rate opens an Add tax rate form.
Name. It appears on the invoice, so use what a client expects to see: "VAT 20%", "GST 5%", "Sales tax 8.875%". Not "Rate 1".
Rate (%). A number above 0 and below 100. Type 8 for 8%.
Price includes tax. Off means the tax is added on top of the price you enter. On means the price already contains it. See Taxes and discounts.
Set as default. Applies this rate automatically to new line items.
The list shows each rate with its Rate, whether it's Inclusive, and which one is the Default.
Using them
On an invoice, apply a rate per line, so one invoice can mix taxed and untaxed items.
On a booking service, attach a rate and the invoices those bookings create carry it automatically. See Pricing and deposits.
That second one is worth setting up. Bookings that create their own invoices are exactly where forgotten tax goes unnoticed.
Editing
The pencil icon on a row opens the rate for editing. Editing changes what future documents use. Invoices already issued keep the rate they were issued with. That's correct, because an invoice is a record of what you charged at the time.
Deleting
The bin icon on a row deletes a rate straight away, with no confirmation. Existing invoices are untouched: each line keeps the rate it was created with.
Services and add-ons that used it stop applying tax. They don't break and you aren't warned, so if you delete a rate, check any service that was using it.
What CoreHue doesn't do
It won't tell you which rate applies, whether you should be registered, or when to file. It applies the rates you set and keeps the record.
Tax varies by country, by what you sell, and sometimes by where your client is. If you're unsure, that's an accountant question, and a cheap one compared to getting it wrong.