Calculating Tax on purchases that include Tax in the total

Calculating Tax on purchases that include Tax in the total

I have decided to not use Books at the present time.
 
One of the biggest reasons is that I am buying and selling items for which the sales tax is inclusive in the price, but I do not have a way to calculate what the tax was from the total price in ZOHO Books.
 
I don't understand why this is not a feature and I don't think that it would require a lot of work to implement.
 
Many businesses buy items at a price with the sales tax included in the total price. My buyers are making a simple sale with little neeed for invoices, etc, but I have to pay the sales tax on that item.
 
I HAVE TO USE A CALCULATOR TO MAKE ZOHO BOOKS USEFUL ?  Ha !