Is it a good idea to convert from a percentile GPA to a 4.0 scale GPA? My school gives me my GPA as a percentage out of 100. If I have 91.55% overall, websites like this and this claim that this is equivalent to a 3.7 GPA. Is it then valid to write on my resume that I have a 3.7 GPA, or would this in some way be misleading or disadvantageous?

Furthermore, if I am able to raise this percentage to 93%, would it be valid to then report that I have a 4.0 GPA?
To raise a 93% to a 4.0 is being slightly dishonest especially if you have a more specific metric. You can always list your GPA out of 100 -  

GPA: 91.55/100


Most employers/colleges understand that not all schools have a grading system out of 4.0