Hi, I was able to replicate the issue with the Total displaying a slightly inaccurate value in the Response Summary for both Constant Sum and Matrix Constant Sum. While I am not sure how to adjust the value that gets displayed for the Constant Sum Total in the Response Summary, you could include a hidden table in a Text/Graphic question on the following page in the survey that will pipe in the accurate numbers and then include CSS in the Question Text's HTML so that this table is not grayed out in the Response Summary for being 'not displayed to the respondent'.

To give it a try, add a page break after the Constant Sum question and add a Text/Graphic Question. Add Display Logic so that this question is never displayed to the respondent (True-False = False). Then, use the Rich Content Editor's HTML/Source view “<>” to update the Question Text with the below, updating the QID at the top with the QID of the Text/Graphic question, and the QID in the table with the QID of the Constant Sum question:

<style type="text/css">
#QID31 > div.Inner > h2 > div, #QID31 > div.Inner > div {
    opacity: 1 !important;
    filter: alpha(opacity=100) !important;
}
</style>
Table:
<table style="width:500px;" cellspacing="1" cellpadding="1" border="1">
	<tbody>
		<tr>
			<td>Option 1</td>
			<td>${q://QID17/ChoiceNumericEntryValue/1}</td>
		</tr>
		<tr>
			<td>Option 2</td>
			<td>${q://QID17/ChoiceNumericEntryValue/2}</td>
		</tr>
		<tr>
			<td>Option 3</td>
			<td>${q://QID17/ChoiceNumericEntryValue/3}</td>
		</tr>
		<tr>
			<td>Option 4</td>
			<td>${q://QID17/ChoiceNumericEntryValue/4}</td>
		</tr>
		<tr>
			<td>Option 5</td>
			<td>${q://QID17/ChoiceNumericEntryValue/5}</td>
		</tr>
		<tr>
			<td>Total Sum</td>
			<td>${q://QID17/TotalSum}</td>
		</tr>
	</tbody>
</table>

Still, the Total that is displayed in the original Constant Sum question should be accurate. I think submitting to Qualtrics Support might be worthwhile.