Using tasklist, list all nginx.exe running on your machine. For that you need to open up a Windows Powershell terminal and run the following command:

 tasklist /fi "imagename eq nginx.exe"

This will give you an output which should resemble the table below:

Image Name PID Session Name Session# Mem Usage
========================= ======== ================ =========== ============
nginx.exe 6696 Console 4 8,724 K
nginx.exe 3156 Console 4 8,988 K
nginx.exe 12156 Console 4 8,420 K
nginx.exe 10724 Console 4 8,744 K

You can then use tasklist again to kill the processes. Notice the column Image Name. We can use that to filter and kill all nginx processes as follows:

taskkill /f /IM nginx.exe

This should kill all the nginx.exe processes. You can use the first command to verify that all of them have been terminated.