Based on prior knowledge, the number of grains per plant (NGL) can be an important factor in determining the grain yield of a soybean cultivar. A higher number of grains per plant usually indicates a higher grain yield.

To generate the dictionary with the requested format, we need to have an understanding of the possible ranges of NGL values for each target class ('low' and 'high'). Let's assume the following ranges:

- 'low': NGL values ranging from 0 to 50
- 'high': NGL values ranging from 50 to 100

Based on these ranges, we can generate a dictionary with 5 typical NGL values for each target class:

```json
{
	"low": [10.2, 20.1, 15.5, 5.0, 30.7],
	"high": [70.9, 80.3, 55.1, 90.0, 60.2]
}
```

Please note that these values are just examples to demonstrate the format and do not necessarily represent the actual distribution of NGL for each target class.