So a couple of links;
Here’s one explaining the idea of using summary/calculations in Monzo Plus Data Export to Google Sheets:
The top half is for a different formula, but similar concept. The bottom half talks about the IFTTT bit.
The same thread then has other good ideas for the Google Sheets thing, and if you keep scrolling past ^ link, you can see some other IFTTT example along a similar theme.
In your case, the formula would be super straight forward; it’s just basically a SUM of all your transactions, and using ROUND to work out the difference to the next £.
See how you get on, but I can come back and help with the formula to do so if it’s of use 