Corporate paying tax at the time of buying an asset.
So why we need to take differenet from corporate book and tax book and calucate the differed tax based on different.

In the Tax Books, you simulate different periodic corporation tax liabilities so that the enterprise could decide which depreciation method to adopt on an asset. The actual depreciation expenses are cptured by the Corporate Books, for the financial statements purposes.
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Bear in mind that depreciation expenses are components to determine the net profit of an enterprise, and as such, opting for a depreciation method which generates lower early periodic depreciation expenses, thus, higher corporation tax in the early fiscal years.
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The periodic Deferred Taxes would the tax variable the enterprise would be be paying more or paying less given the choice of a depreciation method for an assset.
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In order words, the Tax Book environment is where you play with depreciation figures, and you don't want send this figures (accounting entries) to the Corporate Book to mess up the accounting entries in that the Corporate Book, by a way of double accounting entries.

Raghuk2, What you are referring to is the sales tax. Sales tax is handled by Payables modules.
The tax book and corporate book differ in terms of depreciation expense.
Corporations use different depreciation methods for corporate reporting purposes and tax purposes. For tax purposes usually accelerated methods are used. That gives you more depreciation expense in the beginning years and less in later years. Hence you have less income in the beginning years and you pay less tax.