just to clarify, you will have to add an extra $10 to allow tethering on the $60 plan so it would bring you to $70 for tetherable data. you only get 5GB period, meaning the 5Gb allowance with tethering will allow you to tether that 5GB amongst other things but it wont give you extra data that can be used for tethering on top of the 5 you get. all mobile data activity will count towards that 5GB.
it is possible to tether on the $55 unlimited all plan but you will need a workaround. you'll need to look around the forum or google to find out more.
how can you hold someone to a promise they never made to you? - common sense