Your exact tax liability will vary according to your customer and revenue distribution around the world. Different jurisdictions will have different tax levels from low tax regions like South Dakota (4.5%) to high-tax regions like the Netherlands (21%).
This low/high estimate is based on a 80:20 distribution of your revenue in a 4.5% and 21% tax rate, over 12 months.
Low estimate: MRR * 12 * ((0.045 * 0.8) + (0.21 * 0.2))
High estimate: MRR * 12 * ((0.045 * 0.2) + (0.21 * 0.8))
The penalties estimate tends to come to about 10% of the total. This is based on a midpoint:
Penalties estimate: MRR * 12 * 0.1 * ((0.045 * 0.5) + (0.21 * 0.5))