Does a chip retain information in sleep mode?
Yes, RAM is preserved during sleep mode on AVR8s (including the ATTINYs). From the datasheet...



Interestingly, it is even persevered across resets, and seems to even be persevered for as long as the chip is even slightly, slightly powered...

https://wp.josh.com/2014/03/03/the-mystery-of-the-zombie-ram/