Function that can round like this: 10 -> 10, 12 -> 10, 13 -> 15, 14 -> 15, 16 -> 15, 18 -> 20

round.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from django import template
register = template.Library()

@register.filter(name='round_step')
def round_step(x, base=5):
    return int(base * round(float(x)/base))