Why isn't tax being added to my prices on Shopify?

[SimHar07]

Hi All, I am new here, however, I have read a bunch of articles and responses relating to this but I cannot fix the issue. 

All of my pricing imports to shopify from my Inventory system (Cin7) exc tax, this is the price being charged to the customer shopify is not adding tax ontop. 
- In settings i have the "All prices include tax" un checked

- I have set up GST tax for my region

- All products have charge gst checked

- no customers are tax exempt

My store is also charging gst on shipping although this is not checked ?

What else can I try to resolve this?