Hi, @Stacey52. I'll share an insight on your query to help you fix this issue with your QuickBooks Online rounding up.
Since your pension contribution and nest account don't match due to QuickBooks rounding up, you'll want to check your amounts. Thus, rounded numbers can cause discrepancies in some calculations.
Also, QuickBooks Online automatically rounds up the amount since it will be based on flat-rate amounts when calculating. You'll want to ensure that the pension rates are accurate.