Calculation in Excel differs from amount using handheld calculator

I know next to nothing about Excel but am trying to learn and make a worksheet to figure out how much of my Social Security is taxable. There is an online calculator and when I compare my result to that, it's a dollar off. I narrowed down the problem to one cell. I need 85% of the amount in B24. So I entered =B24*.85. The amount in B24 is $13750 and Excel works it out to $11687.36 which it rounds down to $11687. The online calculator gives me $11688. And if I do the math on my handheld calculator it gives me $11687.50 - which would be rounded up to $11688. Where is Excel getting $11687.36? I can't figure it out.