Adding several rows of data to create smaller data set

My title doesn't make as much sense as I could write it currently.

I have a spreadsheet which has approx 800 lines.
That is my main spreadsheet, the values I have in that spreadsheet is the amount of energy used per hour.

In this other spreadsheet I have, it has approx 1k lines, it has the amount of energy provided per 10 minutes (so the data was taken in 10 min intervals instead of hourly intervals).
Since I know that there are 6 "10 minutes" in an hour, I wanted to be able to take 6 rows each (all rows in the same column) and then sum them to convert the 10 minute interval to hour. I've done a few by hand, which isn't ideal for the number of lines I have, I also tried playing around with Group and SubTotal in the Data tab. What should I do to make this way more efficient?

Hello,

It seemed to have worked (comparing it against some of the hand calculations I did), I'm pretty sure it did, thank you!

This is what I had to do though: =IF(MOD(ROW()-2,6)=0,SUM(A3:A8),"") (okay, my actual data is col E, but it doesn't matter). My data starts 2 rows down, it made sense to subtract -2, I got that, when you told me and that the modulus function looks to see if there are any remainders between the row numbers when divided... understood, I guess because my actual data started on the 3rd row and I wanted data up to the 8th row thus making 6 sets of numbers, I had to change it from A5:A10 to 3-8 but still consider the if statement to look at where my actual data starts also.

Now I have a whole bunch of spaces in between those numbers being summed up, what would remove the 5 line spacing?