The ATTiny85 datasheet has this to say about the SRAM while in the various sleep modes:
Idle mode stops the CPU while allowing the SRAM, Timer/Counter, ADC, Analog Comparator, and Interrupt system to continue functioning. Power-down mode saves the register contents, disabling all chip functions until the next Interrupt or Hardware Reset. ADC Noise Reduction mode stops the CPU and all I/O modules except ADC, to minimize switching noise during ADC conversions.
Now, it doesn't explicitly say that SRAM is preserved in power-down mode, but elsewhere it does say:
The contents of the Register File and SRAM are unaltered when the device wakes up from sleep.
Can I assume then that SRAM is preserved (and drawing power), preserving all my variables, even in power-down mode? Thanks.