I have this very simple game that is run by a switch case and in one of the choices I wanted there to be a little mini-game type thing that requires another switch, My qustion is, is that a alright to do? is it bad technique or habit? and if so what would you guys suggest?

...I'd say start off by making the minigame a self contained function()
and later you may want to look into Object Oriented programming styles...

For a simple game, the main loop being a switch statement isn't at all a far-fetched thing. When you get into nesting them, though, you should probably wrap up that inner switch into a function. This'll make the code infinitely easier to read and maintain, as well as prepare you for nastier coding down the road. So:

{//  main loop:  switch (choice)  {    case 0:    //  buy menu    cin >> buyWhat;    switch (buyWhat)    {      case 0:        //  buy thing 0        break;      case 1:        //  buy thing 1        break;      // ...    }    break;    case 1:    //  sell menu    cin >> sellWhat;    switch (sellWhat)    {      case 0:        //  sell thing 0        break;      case 1:        //  sell thing 1        break;      // ...    }  }}

becomes:

{//  main loop  switch (choice)  {    case 0:      buyMenu( );      break;    case 1:      sellMenu( );      break;    //  ...  }}void buyMenu(void){  //  buy menu  int buyWhat;  cin >> buyWhat;  switch (buyWhat)  {    case 0:      // buy thing 0      break;    case 1:      // buy thing 1      break;  }}void sellMenu(void){  //  etc}

Instead of the buy/sell menus, you'd have another function for your minigame(s).

Best of luck!
-jouley