To use cheats in Sim City 5, you must play in a Sandbox region.
Use the following commands while in-game:
ALT+W - Add §100,000 to City Budget
ALT+F - Toggle Fire On/Off
ALT+C - Toggle Crime On/Off
ALT+M - Toggle Health Issues On/Off
ALT+A - Toggle Air Pollution On/Off
ALT+P - Toggle Ground Pollution On/Off
ALT+H - Toggle Homeless Sims On/Off
ALT+S - Toggle Sewage On/Off
Pressing CTRL-SHIFT-C no longer shows cheats.