Please pay attention to what I'm saying. The budget here is voted on by the citizens and it goes up incrementally over time. If the budget was passed and it required $1,000,000 in revenue, and there were 100 of the exact same homes in our town, each home would owe $10,000. If the homes last year were valued at $500,000 then the mill rate would need to be 10% for tax revenue to cover the budget. If this year the value of these 100 homes magically doubled, the mill rate doesn't stay 5%, because tax revenue would be double what the citizens voted for in the budget. The mill rate necessarily must be cut in half because the home values doubled. If this is not happening in your town, go to the town meetings and ask why.
$500,000 x 5% = $10,000
$1,000,000 x 2.5% = $10,000
My home has doubled in value in the past 10 years and when I moved in 10 years ago I paid $8,000 per year in property tax. This year, I will pay $10,500 in property taxes, not $16,000, and that $10,500 represents incremental increases over the past 10 years. Of course, the budget depends on a whole bunch of other issues as well, but if this isn't how it works where you live, you should be asking why?