Question

can chain discounts sometimes be added together

Answer 1

You mean if 5% discount + 10% discount is 15% discount?

Yeah I think it can. Example:

1*0.05 + 1*0.1 = 0.15
and
1*0.15 = 0.15

so they're the same

Answer 2

"Because the discounts occur one after the other (in series), each one has to be calculated in its correct order and not simply added together."

https://www.double-entry-bookkeeping.com/accounts-receivable/chain-discounts/