It's becoming more the norm: gasoline tax changes in July. In fact, it's the second most common month for states to adjust and implement new taxes behind January, when many states see policies kick in for the new year. 
Dozens of fuel tax changes have hit motorists with the start of the new month, and believe it not, they aren't all bad changes: take California, for example. It cut (yes, cut!) its state excise tax on gasoline from 39.5c/gal down to 36c/gal. This should be felt by motorists in coming days. On the flip side, California raised its diesel tax from 10c/gal to 11c/gal. It also adjusted some prepaid tax rates that gas stations must pay before it sells the fuel it buys.
Indiana, on the other hand, saw one of the larger increases in gasoline tax. The state moved from charging a prepaid 16.8c/gal tax to a 22.9c/gal gasoline use tax, which can change on a monthly basis.
Kentucky also adjusted its gasoline and diesel tax, with the diesel rate rising from 25.7c/gal to 28.1c/gal. Gasoline in Kentucky will also likely see a bump up, with the state raising the tax from 28.7c/gal to 31.1c/gal.
Michigan dropped its prepaid diesel and gasoline taxes from 22.4c/gal to 22c/gal.
Maryland raised its gasoline tax from 27c/gal to 27.4c/gal while also raising diesel taxes from 27.75c/gal to 28.15c/gal.
New Hampshire saw its "road toll" raised from 18c/gal to 22.2c/gal.
North Carolina dropped gasoline and diesel taxes from 37.5c/gal to 36.5c/gal.
Ohio added a new tax, called a "petroleum activity tax", which started at an initial 0.65%.
After all is said and done, GasBuddy counts some 15 states which saw either broad or simply localized fuel tax changes. Some of the counties where local taxes were raised included Georgia, Missouri, and Oklahoma, so if you live in those areas and see a bump at the pump, it may indeed be tax related.
With all the fuel tax changes, there seems to be minimal impact on the U.S. national average, which has decreased since June 25. Back in December, GasBuddy warned many motorists that gas taxes in some states were very likely to hit.