Running totals are best done in reporting environments. SSRS handles this cleanly.
If you HAVE to get your procedure/T-SQL to do this, look up the article on this site under 'Quirky Update'. There's other information out there also under the nickname 'Serial Update', and a few others. Running Totals in SQL is another set of keywords.
The Quirky Update article (and ensuing conversations) have some of the tightest, nearly foolproof code to get T-SQL to perform this task... because it's impossible to foolproof it without using a loop otherwise.
Where is the final destination for this data? If it's a reporting environment, I recommend you let them do the Running Total... just for sanity.
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