Using ATtiny 45/85 with HC-05 (Not arduino)
I assume that you wish to implement a "soft" UART on the ATtinyx5 because they do not have a hardware UART. If this is NOT what you want, please provide more detail. 

A UART is relatively easy to implement in software. If you can dedicate the main focus of the program to the UART so timing can be implemented with delays it is quite straight forward. If you have other tasks that occupy significant processor time then use of interrupts helps simplify code. Fortunately, a number of people have already implemented ATtinyx5 UART code and there is a range to choose from. 

Here from 'Garagelab" is what looks like it may be an excellent x5 capable UART as part of a library of other x5 routines. 

Here is avr-softuart on github, with a discussion on using it here.  They use it to talk to an Arduino but that is obviously only an example of what it can do.

Here is another soft UART which may need some modifying for the x5 , but which has a relevant AVRFreaks discussion here

Here is code for a receive only UART for ATtiny85

This search is liable to be useful.