Tax and Customs

I am buying halal goods from different countries and ship them to China, and I have to pay taxes to the Chinese government to import my goods into China, but they ask me to pay a lot of taxes, They asked me to pay 21% of the Value Amount and 4% As Income Tax (From Gross Profit), For Example I buy one thing by 100$, I have to pay $21 as Tax, This is really a huge amount, which means that our profits are very, very limited, and other people who do the same job as us tell the government that they bought their goods at lower prices to pay less taxes to the government, This has enabled them to compete better with us, and it may affect our business, I want to do the same because I really think that 21% is too much, I just want to pay less than not, and as you know China is a non-Muslim country,And I don’t want to lower it so much, Just I want to lower it from 21% to about 18%, Is it allowable to declare the value of goods as less than actual value for the purpose of custom duty and income taxes?

Thank you so much,
With Regards