Nothing wrong with sparging at 90-100*. For batch sparging it is ideal as it helps loosen the mash and rinse the sugars. There are some temps you need to keep in mind.
64-68* is the temp at with the enzymes convert starch into sugars.
78* is the temp that stops conversion
88* is the temp that tannins are released if left for a reasonable period
When you sparge with boiling water you need to remember that it will only increase your mash tun temps by a few *c, so you dont need to worry about tannin release