When any person fails to pay the full amount of the tax required by this chapter, there shall be imposed, in addition to other penalties provided herein, a penalty to be added to the tax in the amount of ten percent or ten dollars, whichever is greater; however, if the failure is due to providential or other good cause, shown to the satisfaction of the Commissioner, the tax may be accepted exclusive of penalties. The $10 minimum penalty levied herein shall be applied only in cases where the payment of tax is not received within the time prescribed in this chapter and shall not be considered for audit purposes. In the case of a false or fraudulent application, where willful intent exists to defraud the Commonwealth of any tax due under this chapter, a specific penalty of 50 percent of the amount of the proper tax shall be assessed. It shall be prima facie evidence of intent to defraud the Commonwealth of any tax due under this chapter when any person reports the sale price of a motor vehicle at 50 percent or less of the actual amount. Interest at the rate of one and one-half of one percent per month, or a fraction thereof, shall accrue on both tax and penalty until paid.