In for a Penny

The phrase "in for penny, in for a pound" is a common English idiom, meaning if one is involved in something even to a small degree, they may as well be fully involved. A common American equivalent states "in for a dime, in for a dollar." The sentiment dates back to at least 1678, when naturalist John Ray stated one might "as good be hang'd for an old sheep as a young lamb," meaning that if one were to be punished for committing either a minor or major crime (here stealing either an old sheep or a young lamb), they may as well commit the more serious one. 

Source: Dictionary.com. (2018). In for a penny, in for a pound. Retrieved from http://www.dictionary.com/browse/in-for-a-penny--in-for-a-pound