Question

that's all right,never mind,it doesn't matter,

that's all right,never mind,it doesn't matter,+not at all,don't mention it它们的区别

Answer 1

that's all right -常常用于安慰某个状况
never mind - 常常用于对方对你做了什么不小心的事
it doesn't matter - 用于向对方persuade 你的看法（positive）
not at all - 客套语，没什么，别客气，哪儿话，不用谢 ( = 美国英语You're welcome.)
don't mention it - 不用介意 or 别这么说 （礼貌的）

Answer 2

same