The Adafruit_GFX class has two methods named print() and println(). These behave exactly like Serial.print() and Serial.println(). Specifically, when printing a float, you can provide a second argument telling it the number of decimal places you want after the decimal point:

display.print(temp1, 1);  // 1 digit after the decimal point
display.print(", ");
display.print(hum1, 1);  // ditto
display.print("%");

The Adafruit_GFX class has two methods named print() and println(). These behave exactly like Serial.print() and Serial.println(). Specifically, when printing a float, you can provide a second argument telling it the number of decimal places you want after the decimal point:

display.print(temp1, 1);  // 1 digit after the decimal point
display.print(", ");
display.print(hum1, 1);  // ditto
display.print("%");

Background: the reason these methods behave like the ones of Serial is that both Adafruit_GFX and HardwareSerial inherit them from the Print virtual class.