No they actually can't. In stocks the price is publicly listed by a third party. In real estate an assessor gets involved. For commodities like cars they have to be unique or nearly so before there isn't a third party listing it's value.

For edge cases, especially large real estate, we could always make a second law, one that says the government can buy your building at the value you gave the IRS if it's significantly below market rate on dollars per square foot for it's type (office, industrial, residential, etc), or that it's represented as a higher value in investment reports or bank loans. We'll frame it as a bail out, helping them offload toxic assets. Then the government sells the building on the open market. That way when someone like Trump decides his buildings are suddenly worth less than all of the surrounding buildings we can keep him from going bankrupt again.