The man is described as about 1.82m tall (6ft), of medium build.
He was wearing black shoes with white soles, blue jeans and a black hoodie with bands on the arms.
He wore a light-coloured balaclava and gloves.
Mr Singh said the incident was all over in a matter of minutes.
"I was sweeping the floor and my mate was mopping up when he came into the shop.
"My mate ran out the back when the guy tried to attack him, then he swung a knife at me a few times.
"I tried to defend myself with a broom - the guy tried to stab me twice and I was fighting with him and the broom slipped out of my hands - I had no choice in the end but to give him the money."
He said he had had a few arguments with people in the store, but had not been robbed for at least three years.
"I've faced this sort of thing before, so I wasn't scared, there was no fear, but he got the cash and then just ran away."
Mr Singh said he was back at work the next morning.
"I opened up the shop like normal and people from the neighbourhood came in asking if they could help.
"They look after us here and we really appreciate that from them, most of them are really nice."
He said the attack was quite upsetting, especially for his co-worker, but they were both back at work the next day thankful they were not hurt.
"It's not good, he took a lot of cash, but we have to keep working," he said.
Police would like to hear from members of the public who witnessed what happened or saw someone matching the man's description.
Anyone with information relevant to this investigation can contact Rotorua police on (07) 348 0099. Alternatively, information can come anonymously via Crimestoppers on (0800) 555 111.