Calculate tax programmatically in magento for some customers

Question

my products price are inclusive of 12.5% tax so if my customer has tax excempt then he should not pay 12.5% instead he should pay 2%.

tax excempt:- if my customer produce c form then he is applicable for 2% instead of 12.5%.

Here is my code

i have observer called sales_quote_collect_totals_before

if($customer->getIsTaxExempt() == 1)
{
    $items = $observer->getEvent()->getQuote()->getAllVisibleItems();
    foreach($items as $item){
        $item->getProduct()->setTaxClassId(0); // set product tax class to none
        $basePrice = $item->getProduct()->getFinalPrice() / (1+(12.5/100)); // $basePrice is my price exlucive of 12.5%
        // here i want $basePrice + 2% of the $basePrice as my finalproduct price inclu of tax
        $item->getProduct()->setTaxClassId(12); // set product tax class to 2%
    }
}

but this is not working.prices are not changing in the cart.

Note: My code is going into if statement required customers.

Answer 1

I had done this with myself by adding custom logic in the sales_quote_collect_totals_before observer

public function newTax($observer){
    $quote = $observer->getQuote();
    foreach ($quote->getAllItems() as $quoteItem) {
        if ($quote->getData('customer_cform') === 'true') { // check if customer is b2b customer and selects for the cform option
            $product = $quoteItem->getProduct();
            $product->setTaxClassId(0); // tax class removed.now the price is with no tax
            $basePrice = $product->getFinalPrice() / (1+(12.5/100)); // calcuated 12.5 % of total price and subtracted from the price to get base price
            $final_cst_price = $basePrice * (2/100); // added 2% in the base price to get fincal cst price
            $finalPrice = $basePrice + $final_cst_price;
            $product->setPrice($basePrice);
            $product->setTaxClassId(8); // here 8 is a tax rule defined in the magento admin just to show the split of base price and tax (2%) in the cart page and checkout page
        }
    }
}