Claims of $300 or less do not need written evidence, you can make reasonable estimates however the ATO may ask you to explain why your claim is reasonable based on your occupation.
If your Work Related Expenses are over $300 you will need to provide written evidence for example tax invoice; evidence of payment from bank statement or original receipts. The ATO website states that if your work related expenses are over $300, you can record evidence of the expense yourself if the "expenses of $10 each or less, providing the total of these expenses is not more than $200"
All work related expenses must have been actually incurred and not reimbursed.
Nothing showing the original post was specifically for investment properties. Not sure if you could apply the ATO's ruling for no receipts from work-related expenses for rental income expenses¿