It's my understanding where the sale takes place is what determines what/which sales tax is used and for Fellers, that would be Kansas, where the sales tax would begin. However, going across state lines, nixes most everything out.
My question would be, what kind of items are you buying from a supply house which requires you to pay tax in the first place.
Anyway, do you, yourself have a tax exemption number and if so, why aren't you using it ??
If you do... and you're paying taxes on various things and then charge your customers sales tax, that's considered double taxation which is illegal in all 50 states regardless of what anyone thinks.