J.Racenstein does not collect Pennsylvania sales tax. Therefore, you may be required to remit use tax directly to the Commonwealth on your purchase if the items are subject to Pennsylvania sales tax.
Back in 1992, the Quil Corp vs North Dakota case prevented states from collecting any sales tax from online purchases unless the business had a physical presence in that state. However this year, South Dakota vs. Wayfair overruled the outcome of the Quil Corp case. Now states can charge tax on out-of-state purcahses even if the business does not have a physical presence. Read this post regarding the case.