"roughly a hundred" is a perfectly correct and usable phrase in written English.
For example, you might write: "There were roughly a hundred people in attendance at the meeting."
In 2011, this amounted to roughly a hundred American dollars.
They made it roughly a hundred yards before being cut down by an Apache helicopter.
(The software makes sounds based on roughly a hundred different parameters).
Roughly a hundred meters behind the sandbags lay more road barriers: overturned trash containers, wheelbarrows, stones.
That process should end up filtering roughly a hundred events per second for later detailed analysis.
(The company followed through, relocating and moving roughly a hundred jobs to Cheyenne, Wyoming, in 2015).
Reiman said roughly a hundred million dollars.
Last year, Blue made roughly a hundred thousand dollars, and paid some ten thousand in taxes.
In an average year, roughly a hundred thousand Americans are killed or wounded with guns.
The most popular one occupied readers for 3.6 billion seconds, or roughly a hundred and fifteen years.
The length of each book is fixed at thirty-five thorsand woroughly roughly a hundred and twenty pages.
