Cialis tablets are almond-shaped, meaning that they are hard to split accurately, although this isn't as critical as other drugs. In this case, though, splitting the 20 mg tablets may not actually save any money. In the pharmacy where I work, 30 days worth of the 5 mg strength is about 140 dollars, about equivalent to buying 10 20 mg tablets. It would be worth saving the headache of splitting the pills to me to save the few dollars a month. (The 2.5 and 5 mg daily tablets are the same price, and the 10 and 20 mg as needed ones are the same price as each other as well.)
Also, ask your MD about a coupon for your first month, I have seen one-time use coupons come through that cover an entire month of the daily Cialis.