Is there anything wrong with this mysql trigger?

Question

I have a product, sales_order, and sales_order_product table.

The nature of the products dictate frequent changes to price and weight.

The customers often times save orders for a few days before submitting and paying for them.

Because of this lag and the price/weight fluctuations, we allow them to freeze in the price/weight at the time of the original order.

We save the order amount (subtotal), sales tax, order weight, among a few other things in the sales_order table.

I know it's not recommended to have any business logic within the database layer though I see this as more of a means to maintain referential integrity.

Below is one of the triggers I use to calculate the aforementioned data. I've only started to test it out and so far so good. Performance wise, I haven't seen any issues thus far but my testing hasn't been very extensive.

Is there anything about this trigger that doesn't look right? I ask because though I've used triggers for things like time stamps I've never really used them in this capacity (and considering we are talking about money, I don't want to screw something up that could lose me my job).

I realize it's probably not a good idea to hard code the tax rate, and I'll probably change that when the time comes.

CREATE TRIGGER after_sales_order_product_update
AFTER UPDATE ON sales_order_product
FOR EACH ROW
BEGIN

    SET @product_amount = (SELECT SUM(quantity * unit_price) 
                           FROM sales_order_product 
                           WHERE sales_order_id = OLD.sales_order_id),
        @product_discount = (SELECT SUM(quantity * unit_discount) 
                             FROM sales_order_product 
                             WHERE sales_order_id = OLD.sales_order_id),
        @total_weight = (SELECT SUM(quantity * unit_weight) 
                         FROM sales_order_product 
                         WHERE sales_order_id = OLD.sales_order_id),
        @tax_amount = ROUND(@product_amount * 0.0975,2);

    UPDATE sales_order 
    SET product_amount = @product_amount,
        product_discount = @product_discount,
        tax_amount = @tax_amount,
        total_weight = @total_weight,
        product_total = product_amount - product_discount
    WHERE sales_order_id = OLD.sales_order_id;

END