Is better to keep the thermostat at a constant 75 and raise it for showers to 77, then keep it there until it satisfies, then return it to 75. OR, is it more economical to keep it at 72, raise it to 77 when feeling chily, then return it to 72?

For the greatest efficiency, it's actually recommended to set your winter thermostat to 68°F and adjust it down when you sleep or leave your home for several hours. According to ENERGY.GOV - It's tempting to leave the thermostat on at a set temperature, so that the room is warm when returning home. Many assume this saves energy, because the heater won’t have to work as hard to heat the room to the desired temperature. It's actually more efficient to heat your home just as you need, which means turning the heat off or down when you leave the house, or setting your programmable thermostat to do so if you have one. Did you know that you can save around 10% on your heating bills by turning your thermostat back 10°–15° for eight hours? For more articles on this subject, go to: https://www.energy.gov/search/site/winter%20thermostat%20setting?f%5B0%5D=bundle%3Aarticle

Looks like Mr. Alexander answered your question. Thank you for asking!

The best is to your thermostat the same temp if 75 is a comfortable temp. Then keep it there its more economical to a constant temp then it is to keep moving it around