No difference, just that when you said “I have a bill for $150” I assumed that you had received the bill, not sent the bill.
It would appear that the Sales Tax is a Custom Code created by you and that creation contains a setup error. Note how the Tax Payable balance is 7.38 which is 7.375 rounded.
It would appear that you may have ticked a flat rate tick box - untick it and what now occurs.
Otherwise post a screenshot of that custom tax code dialog panel.
Just an aside: Sales Orders are only required if a customer sends you an order, you don’t need to create one to create a sales invoice.