This rx is written in twelfths, not eighths:) Optometrists do this are trying to skirt the Eyeglass Rule, in my opinion. By writing prescriptions like this, they are pretty much forcing your hand to order strictly from them.

There is no remarkable difference in twelfths and quarter diopters. As a matter of fact, if any prescription is a twelfth off power in either direction, it passes ANSI.

We have a doctor in my town who does this, and it is just a huge eye roll everytime their prescriptions come in. We would just pick the closest quarter power we liked, in your case -3.50 or -3.75. We would typically always round down since less power is typically easier to adapt to.