It turns out that snack foods like Twinkies and Pop-Tarts are tax-exempt in Manitoba, alongside grocery staples like vegetables and meat.

Quiz

Scroll down and take the quiz at the bottom of this story. See if you can tell which foods are tax-exempt or not.

The list of basic grocery products that are tax-exempt across Canada, including in Manitoba, includes fruits, vegetables, meat, fish, poultry, breakfast cereals and some dairy products.

But a closer look at the basic groceries list reveals that Twinkies snack cakes and Pop Tarts toaster pastries are also not subject to the GST or PST.

That has Winnipeg dietitian Phyllis Reid-Jarvis wondering if governments should reassess what should be on the tax-free list.

Pop Tarts and Twinkies have no health benefits, Reid-Jarvis said, and making them tax-exempt does not promote healthy eating.

"I don't know what the government's intention was, but I could discern … you're making it easier for Manitobans to make those poor eating choices," she said.

Woman taxed for bag of potatoes

CBC News examined the lists of tax-exempt grocery products after a Winnipeg woman said she was incorrectly charged both the GST and PST on a bag of potatoes at a local Wal-Mart last week.

Pam Treller

Pam Treller of Winnipeg says she was surprised when a local Wal-Mart store levied tax on a bag of potatoes she purchased last week. (CBC)

"I expected to pay $3.25, but it came to $3.50," said Pam Treller.

Treller said the store manager told her the potatoes were not on the list of tax-exempt basic grocery items.

Wal-Mart admitted that it was an "isolated incident" that was corrected in 24 hours. As well, Treller was offered a refund, the company said.

"We take this issue very seriously and wish to apologize to the customer for any inconvenience we have caused," a company spokesperson stated in an email.

But Treller said the provincial government should fine Wal-Mart for the mistake and look more closely at what taxes are being charged.

"It makes you wonder what else they're charging on," she said.

Provincial tax rules mirror federal rules

In an email to CBC News, a Manitoba government spokesperson said the retail sales tax "parallels federal GST rules to simplify the tax application for both the retailer and consumer."

Pam Treller's receipt

Pam Treller's receipt shows the GST and PST charged. Wal-Mart officials said it was an "isolated incident" that has since been corrected. (CBC)

A Manitoba Finance bulletin on the Retail Sales Tax Act indicates that "sweetened baked goods" like cakes, pies and donuts are on the list of tax-exempt basic groceries, provided that the products sold exceed a single serving or contain six or more single servings.

However, sweetened baked goods that are "sold to consumers in quantities of less than six items, each of which is a single serving of less than 230 grams" can be taxed, according to the bulletin.

Among the snack foods that CBC News found were tax-free were an eight-pack box of Pop Tarts, an eight-pack box of Twinkies, and a package of nine chocolate banana muffins.

Snack foods that are taxable include candy, marshmallows, potato and corn chips, cheese puffs, salted nuts or seeds, fruit-based snack foods, single servings of chocolate milk — plain milk is exempt — and granola products that aren't sold as breakfast cereal.

Federal health officials did not respond to a request for comment on Tuesday.

Officials with Food Matters Manitoba, a group dedicated to food security, say they're against raising taxes for junk food because it would create a burden for low-income families, which tend to buy junk food because it's generally cheaper than healthy food.

Quiz: Taxable or tax-exempt?

With files from the CBC's Sean Kavanagh