This has been discussed already on this forum a couple of months ago when Aliexpress started doing this. It only applies to sales to Australian customers. And it's so rare in the U.S, I personally have yet to come across it.
then should I pay the tax and request the aliexpress tax back?
The fact that they collect it means that they are the ones who pay it. It's the same story with eBay and Amazon.
My question is .. should I start collecting tax as well? If I start collecting tax as well then should I pay the tax and request the aliexpress tax back?
Search this forum. I'm not going to go over it all again. But in a nutshell, the consensus was to "Not worry about it and let your overall profits absorb it, and don't charge your customers for it." In Australia you only pay GST once your sales are over AU$75,000 per year. Then and only then should you worry about the tax Aliexpress has already collected. It depends on what country you live in.
Use Google for more details relevant you, depending on what country you live in. I live in Australia and researched the Australian Tax Department site.