Don’t spoil the ship for a ha’p’orth (halfpennyworth) of tar

Don’t risk the failure of a large project or spoil the look of something by trying to economise on trivial things.

e.g. We are having our kitchen re-fitted. My wife has chosen cheap cupboards. I think it’s worth paying for better ones; I don’t want to spoil the ship for a ha’p’orth of tar.

The idiom was originally to “lose a sheep, or a hog, for a (half)pennyworth of tar” - for want of spending a trivial sum on tar—with reference to the use of tar to protect sores and wounds on sheep from flies.
The spelling ship represents a local pronunciation of sheep. Because of this similarity in pronunciation, non-countryfolk obviously assumed that the expression referred to a ship, the assumption being reinforced by the reference to tar, which was widely used on wooden ships to coat and preserve the timbers.