Power Query number rounding issue

1. =ROUNDUP(([@Cancelled]-[@ACCEPTED])*1440,"1:00") - "1:00" is a character, hence it will be treated as 0 in Excel. Hence =ROUNDUP(([@Cancelled]-[@ACCEPTED])*1440,0) will give the same result.

2. Now, below are results for [@Cancelled]-[@ACCEPTED] in Excel and when this is multiplied by 1440.

Below screenshot is from Excel

Now, you see the second result is 299.00000000023200. Excel's precision is 15 digits. Now, if you count 15 digits, the number would be 299.000000000232. Since Roundup is detecting 232 after decimal places, hence Roundup is making 299.00000000023200 to 300.
3. This behaviour is same in DAX also. Hence, DAX and Excel behaves the same.

4. See the below for results of Current-Accepted (This screenshot is from Power BI Desktop)

Now let me use Windows supplied calculator for second row values

DAX - 0.207638888889051*1440 : 299.0000000002334

PQ - 0.207638888888889*1440 : 299.0000000000002 

Now, in case of PQ when I count 15 digits, it comes out to be 299.000000000000. This is quivalent to 299, hence no effect due to Roundup. 

Hope, it clears up the issue for you. 

I will also suggest you to read Floating point Airtmetic issue of Excel - https://docs.microsoft.com/en-us/office/troubleshoot/excel/floating-point-arithmetic-inaccurate-result 

The second argument of Number.RoundUp is “digits” – the number of digits to round to. Replacing the 1 in your formula with a 0 will fix the problem.

Number.RoundUp( 
   Duration.TotalMinutes( [Cancelled]-[Accepted] ),
   0
)