Three online retailers have signed to the Pennies microdonation scheme including Party Pieces, the business run by the Duchess of Cambridge's mother, Carole Middleton.

Party Pieces is taking donations for the Rainbow Trust Children’s Charity, BuySpares (an online retailer of spare parts for appliances) is supporting the John Taylor Hospice and Contact Lenses Express is supporting RNIB.

Carole Middleton said of the Pennies scheme: “I think this is simply a brilliant idea which I hope everyone else will get behind.”

Rainbow Trust chief executive, Heather Wood said: “This is a really innovative way to get donations through online shopping. Their support will make a real difference to the children we work with.”

This brings the total number of retailers supporting the initiative to 11 and number of charities benefitting to 28.

Pennies works with retailers by asking shoppers to round-up their bill to the nearest pound to donate to charity. Three quarters of the donation goes to the retailer’s chosen charity (or charities) and the remaining 25 per cent split between charities chosen by Pennies.

Alison Hutchinson, chief executive of Pennies said: “We’re thrilled that these new retailers are joining the Pennies movement and demonstrating how simple and quick Pennies is to introduce in an online environment.”

So far more than £435,000 has been raised from more than 1.7 million individual donations and last month Dominoes, which was the first retailer to sign up, reached 1 million donations.