I would include VAT. No matter B2B or not, it's how much your end customer pays is what matters. Yes, business will pass on this tax further, but end consumer won't be able to claim it. It's the same as a sales tax in the US. To include it in price or not is more a psychological thing (in the US it's not included in price). When I pay $106.25 for something it makes a little difference for me that $6.25 goes to my state or passed to the previous business, and if I only have $100 you lost me. That's the reality.

Basically it's very similar to debates about US taxes. Sure, it's not 70%, but things add up quickly. Income tax, social security, medicare, medical insurance, sales tax. The usual argument is "but, but ... it's not me who is paying my medical insurance or half of social taxes, it's my employer, so it's not my tax". Well, it is. That's the money your employer would have paid _you_ if those taxes hadn't existed.