Criminal Sentence 393: Less Lesson

From a book I'm reading:

“Worse, having been promised some lowering of the high wartime land taxes, the Parliament men were clamoring to pay less taxes, not more.”

I'm surprised this slipped through. I know we all use "less" when speaking informally, but in writing we need to be more grammatical, not less.

"Less" goes with uncountable items, such as sugar and milk.
"Fewer" goes with countable items, such as cookies and vegetables.

You pay less tax but fewer taxes.