I was able to determine the root cause of this but it still may represent a 'bug' of sorts with the May 2021 version of PowerBI Report Server.
The calculated measure in question is pulling data from an Excel file, which has numbers in decimal format. When importing the Excel data into PowerBI via query, the decimals populate. However, the Data Type was set as 'Any'. When the data pulls into PowerBI from the query, the numbers are represented as Whole Numbers, not decimals. The rounding logic seems to work correctly at this point when determining the whole number conversion.
This process seems to break down once the report is published the the Power BI Report Server web portal. The rounding logic does not seem to carry through and this is when we notice differences in our expected sum totals between the version published to the web portal and the version running in the PowerBI desktop application. All decimal numbers seem to round down to the lowest single integer.
The solution was to change the Data Type to 'Decimal' in the query coming from the Excel file. Once this was applied, all logic seemed to carry through once published to the PowerBI Web Portal. The problematic values were rounded correctly in both the application and web portal.