Could use more details on what this means exactly

We only actually perform a cascade using the level two tax. So 'level_2_tax_amount' = (price + level_1_tax_amount) * level_2_tax_rate, whereas level_1_tax_amount = price * level_1_tax_rate. If level_2_tax_amount is calculated before level_1_tax_amount it will substitute 0 so level_2_tax_amount = (price + 0) * level_2_tax_rate. Not really sure how to clarify this. The calculation for level two thinks there is no tax for level one if level one has not been calculated yet. Just a matter of fetching the tax rules from the database in the right order.

It sounds like there is an issue with the calculation order then. Have you looked at the pricing presenter to see how it handles cascading taxes?

price = sum(items)
level1_amount = price * level1_rate
level2_amount = (price + level1_amount) * level2_rate
total = price + level1_amount + level2_amount

Have you looked at the function I mention in the task? It uses one query to fetch both level 1 and level 2 tax rules, then loops through them, calculating the amount for each. No I didn't look at the pricing presenter, but it must of course follow the progression you list. When the taxes are retrieved in the right order getTotal() does it in this form:

price = sum(items)
level1_amount = price * level1_rate
tax_total = level1_amount 
level2_amount = (price + tax_total ) * level2_rate
tax_total += level2_amount 
total = price + tax_total

This is a super simple fix. Just needed to add an order by to make such the rules are fetched in the right order.

You should create tests that show this problem not working correctly and your fix resolving it. It would be useful to have unit tests for this method if there aren't any already so we can continue to ensure it works correctly.