I’ve a Revolut account as well, and their round-up feature has an ‘accelerator’, allowing for faster saving.
1 x Accelerator
£2.70 transaction, rounds to £3, 30p saved
3 x Accelerator
£2.70 transaction, rounds to £3, 3 x 30p = 90p saved
I imagine this feature will probably be quite easy to add into the current Monzo Round-Up operation - the fact that Revolut has it is just about the only thing keeping me using them as my main account spending (awwwwwful customer service).