This depends on how the products are used by the purchaser. By law the sales tax is based on the delivery address.
This works well for obvious cases where a counter top is delivered to a home. (a specific address).
But if you are charging sales tax for a contractor, who is now going to use that product at a job site at various locations through out the state, then you have no way of knowing where the product is to be used.
Technically, if you deliver the product to the job site, then you would charge sales tax for that delivery point.
If the customer is coming to your site to pick up the product, technkically the product is delivered at the point of sale. it is taken posession of there. So you would be correct to assess sales tax a the point of sale.
What happens however, is that the customer is responsible for use tax based on the difference of rate from the county in which the product is to be used.
It looks to me like your company is considering the product delivered to the purchaser's address, when it is picked up.
Techically, you are correct.