Cash registers in the US have always been perfectly happy to add sales tax (sometimes two) without any previous notification to the purchaser [illegal in the UK]
In the UK when the sales are business to business transactions, it's fairly common for displayed prices to be shown exclusive of VAT and for the tax to be added on at the till so I can't see any reason why the airside tills couldn't be programmed to deduct the VAT before the final price is shown.