Can you have a system that works with only one PST account?

I have taken over a system that has been setup all wrong and I am trying to fix it.  In ever system I have worked on in the past I have always had a PST account for Sales and one for Purchase.  I noticed today that for some strange reason that this system has only been setup with one PST account, 2300.  It has the two accounts for GST.  This is for a non-profit bar, so 95% of the sales are LST in that it is 10% PST here.  I only came across this by fluke as I was attempting to figure out an issue I am having with their inventory and found some postings from AccuPos that only had GST and not PST.  I dug a little more and found the sole PST account thing.  I find it odd that there is only one PST account.  It could explain why they have had issues with the AccuPos too as there has been a tax coding issue.