Well full cycloplegic refraction(after pupil and accommodation relaxation) objective power is estimated, which guides for subjective correction. Blurring of vision experienced due to power is actually in excess of natural compensation changes in eye, minimal power are naturally corrected by eye lending clear vision but may cause symptoms due to constant strain in form of headache,eye pain,burning etc. While prescribing glasses it is important to nullify these compensating strain from eye to prevent fatigue and constant clear vision. 0.25 D +/- the actual power is fine, usually they match well. High or less depends on your other eye power,your age, working distance etc. You can pick high or less subjectively and can also use confirmatory test like duochrome test for spherical and astigmatism fan test for cylinders. I suggest to visit ophthalmologist for cycloplegic refraction if possible and comfortable glasses. Regards