No one method of accounting is prescribed for taxpayers. Each taxpayer shall adopt the methods, forms and systems that best suit his needs, so long as they clearly reflect income. A method of accounting which reflects the consistent application of generally accepted accounting principles in a particular trade or business in accordance with prevailing conditions or practices in that trade or business shall be presumed to clearly reflect income, if the method is used for Federal income tax purposes.
61 Pa. Code § 101.2