What is the real purpose of the Net Amount Inclusive of Tax option in the Tax Type record (SuiteTax is enabled)? I thought it would allow me to enter a tax-inclusive amount like in credit card transactions from bank feeds, and then NS would automatically calculate tax amount? For example, in AU, if I enter an Amount of 110 which is the gross amount, then NS will set the net amount to 100 and the GST to 10 automatically when a tax-inclusive Tax Code is selected.

It's more about how NetSuite calculates the base for percentage taxes. It's not automatic gross-to-net splitting like you expect. For bank feeds with tax-inclusive amounts, you would need custom scripting or use tax-inclusive item setup instead. The native tax engine assumes net entry, not gross.

But I've already used a tax-inclusive item setup and it's not working.