Is there a bank that will give you a debit card and rounds up your purchases and puts that extra money into a separate account?

That makes no sense.  Since a debit card takes money directly out of an account, what you are suggesting would simply move move that money from one account to another.  Why not just move some amount of money yourself every month?

Bank of America had it, and may still. It's really pretty useless for savings and is more of a gimmick. And, credit cards used responsibly and paid in full each month as cycle ending balance raises a credit score, protects money better, gives rewards. I only use my debit card as an ATM withdraw for cash and never make a debit card purchase. 

there are some that  do

https://www.halifax.co.uk/bankaccounts/help-guidan...