Challenge:

Given two inputs, x and y, round x to one less significant figure, then repeat until it has y number of unrounded digits left. (the decimal point does not count as a digit)

Input & Output

Input can be a combination of strings and integers, e.g. you can have the input as a string and the output as an int, or vice versa.
The input number will never have 15 digits total, and the y will never be greater than the input number's length and will always be greater than 0.
Example:

x = 32.64712, y = 3
32.64712 -> 32.6471 -> 32.647 -> 32.65 -> 32.7  (Three unrounded digits left)

x = 87525, y = 2
87525 -> 87530 -> 87500 -> 88000 (Two unrounded digits left)

x = 454, y = 3
454 -> 454 (Three unrounded digits left)


(steps shown just to clarify, you only need to output the last value.)

Rules

• Trailing 0's are allowed
• 5's round up
• Standard loopholes apply

This is , so you should strive for the shortest answer.

• I take it numbers ending in 5 round up? If we get a result like 3.100, do we have to output the number with trailing zeroes? – xnor Dec 12 '18 at 4:53
• The phrase "round x's second to last digit" seems ambiguous and I'd interpret it differently from what the challenge intends. I'd call it "round away x's last digit" or "round x to one less significant figure". Also, the input refers to integers, but the numbers can be non-whole reals. – xnor Dec 12 '18 at 5:00
• @xnor Numbers ending in 5 do round up, trailing zeros are ok – Embodiment of Ignorance Dec 12 '18 at 5:10
• Ugh, JavaScript rounds 32.647 to 32.64999999999999857891 which is still less than 32.65 ;-( – Neil Dec 12 '18 at 9:47
• For javascript, you can scale the number up so that there are no digits right of the decimal point, then divide it down after scaling(since integer math is exact) – Embodiment of Ignorance Dec 12 '18 at 18:19

Python 2, 101979291 85 bytes

lambda x,y:reduce((lambda n,l:int(n/.1**l+.5)*.1**l),range(15,y+~len(int(x)),-1),x)


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Alternative : If Python's round would round "half up" instead of "half to even":

Python 2, 57 bytes

lambda x,y:reduce(round,range(15,y-len(int(x))-1,-1),x)


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Perl 6, 59 bytes

{($^a,{.round(10**($++-15))}...^0|any 10 X**^30-15)[*-$^b]}  Try it online! Anonymous code block that takes two numbers and returns a number. Explanation: { } # Anonymous code block ( ... ) # Create a sequence$^a,   # With the first element as the input
{                    }  # With each element being
.round(10**($++-15)) # The previous element rounded by another digit 0 # Until 0 | # or any 10 X**^30-15 # Any available power of 10 ^ # Ignoring the last number [*- ] # Index from the end$^b   # The second number


JavaScript (ES6), 58 bytes

f=
(x,n,y=x.toPrecision(n))=>y>x?y:(x*9/8-y/8).toPrecision(n)
<div oninput=o.textContent=f(+x.value,+n.value)><input id=x><input id=n type=number min=1 max=15 value=3><pre id=o>

Arithmetic solution. The given procedure rounds numbers up if they are greater than 4/9 of the next value, so if rounding doesn't increase the number, try again with a slightly greater value.

R, 79 bytes

Unfortunately, R uses "round to even" when rounding off a .5

function(x,y){for(i in nchar(gsub('\\.','',x)):y){x=signif((x*100+1)/100,i)};x}


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