Reporting sums of shopping carts
First of all i think making a view in your database which sums your needs will be better because generally sql engine sum operator's performance is way better than lopping values in programming languages.

Second if we go through your code:
You have done mapping for all objects one by one. Java stream mapping is similar to for loops in compile time. So here what you make is similar to creating for loop foreach object which is bad for performance. 
To be performance wise you can create one for loop and generate your sum values in it. 

Note: BigDecimal is the preferred way to store double money values in Java