Hi,
That's strange. If you're using the TaxCloud plugin by default in HikaShop to calculate the taxes automatically, the text you should see should be "Tax (%s)" where %s is replaced by the actual tax rate.
This comes from the translation key TAXCLOUD_TAX which is on line 2139 of the English translation file of HikaShop:
TAXCLOUD_TAX="Tax (%s)"
You can check your translation file via the Languages tab of the HikaShop configuration page:
www.hikashop.com/download/languages.html#modify
Also, you can use a translation override there to change any text of the interface, including that one.
But maybe you have the "detailed tax display" setting turned off in the HikaShop configuration ? In that case, it would use the translation key VAT, which is indeed VAT in the en-GB translation file of HikaShop, but it "taxes" in the en-US translation file of HikaShop for US-based websites. So maybe you have that setting turned off and you're using the en-GB translation file ? In that case, you could either turn that setting on, or use the en-US language, but you could also just do a translation override as explained in the link above.