How much sovereignty is forfeited with EU membership?

The EU has ruled: that Apple Must Pay Ireland $14.5 Billion In Taxes, that Ireland gave Apple illegal tax breaks.
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Seems to me the EU is interfering with Ireland’s efforts to attract business, to the detriment of Ireland.

How much sovereignty is forfeited with EU membership?

EU bureaucrats (European central authorities) are now overseeing tax policy and rates for member countries. Here they’re imposing their policies retroactively seeing fit to take money from a company going back many years, even though the company had negotiated a contract with the country in good faith.

Do the Irish people have any say in the matter? Do they have any influence on the decisions made by the EU bureaucrats?

When will Irexit happen?