Based on my prior knowledge, the Number of legumes per plant (NGP) can potentially affect the grain yield of soybean cultivars. Generally, a higher number of legumes per plant suggests a higher potential for grain yield, while a lower number may indicate a lower yield.

Therefore, I will analyze the relationship between NGP and grain yield to determine the appropriate ranges of NGP values for the target classes 'low' and 'high'. 

After the analysis, I will create a dictionary that includes 5 typical NGP values for each target class.

Note: It is important to note that without specific data, the analysis and resulting dictionary will be based on general knowledge and assumptions.

```json
{
	"low": [1.5, 2.0, 2.5, 3.0, 3.5],
	"high": [4.5, 5.0, 5.5, 6.0, 6.5]
}
```

In this dictionary, the possible values of NGP for the target class 'low' are [1.5, 2.0, 2.5, 3.0, 3.5], while the possible values of NGP for the target class 'high' are [4.5, 5.0, 5.5, 6.0, 6.5].