Question Concerning Sales Tax:

• A. Zaid sold a product to a customer and took ten dollars in taxes. For example, an item which cost $100, he added $10 taxes and took $110. However he declared $90 to the Government. What is the ruling of this case?
• B. Zaid ordered a hundred thousand dollars in merchandise and declared fifty thousand to the Government. Is this permissible from a Shar’ee perspective?

Answer:

• A. His declaration of the price at $90 to the Government is a lie and deception, which is haram (prohibited in Shariah).
• B. This is a lie and deception, which is haram (prohibited in Shariah).

And Allah Ta’ala knows best.
Mahmoodul Fatawa Vol.5 Pg.429-430