Nearest multiple of 10

class Solution {

    String roundToNearest(String str) {
        StringBuilder ans = new StringBuilder(str);
        int n = str.length();
        int t = (str.charAt(n - 1) - '0') % 10;
        if (t <= 5)
            ans.setCharAt(n - 1, '0');
        else {
            ans.setCharAt(n - 1, '0');
            for (int i = n - 2; i >= 0; i--) {
                char ch = ans.charAt(i);
                if (ch == '9')
                    ans.setCharAt(i, '0');
                else {
                    ans.setCharAt(i, (char) (ch + 1));
                    break;
                }
            }
        }
        return ans.toString();
    }
}