Why do you not use the build in ROUND function?
It takes three parameters:
- the value
- the rounding length (use negative numbers to round to a power of 10, example for 12345: -1 ->  = 12350, -2  -> 12300, -3 = 12000
- optional 0 or 1, while the default 0 rounds, while 1 will cut the numbers off; ROUND(12345, -1, 0) = 12350 while ROUND(12345, -1, 1) = 12340

The only benefit of your function is the easier usage of the direction (up or down), but this could be solved by cutting off the decimals (= rounding down) and adding 10 (or 100 or 1000...) when you want to round up: ROUND(12345, -1, 1) + 10

PS: Bonus points for using an INLINE TABLE VALUE function instead of a scalar function