PA use tax is being calculated as 0 on turbotax

Entered purchase prices and description (for online purchases where websites didnt charge sales tax). Total purchase price is a non zero number but on the next page, turbotax shows

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Based on what you told us, here's how everything worked out:
Total Use Tax
$0.00
Additional Estimated Use Tax from Optional Table
,
Minus: Sales Tax already paid
$0.00
Pennsylvania Use Tax Due
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As you can see. It shows the Total use tax as 0 and also Pennsylvania Use Tax is blank (just white space)
 
My questions. Is the software miscalcuting and showing me wrong info or there are any rules that I am not aware of , because of which the purchases of this amount are not taxed?