Hi, I would use this method to achieve adding the trailing 0s. This will append a 0 up to 4 decimal places regardless of the rounding length.
For example you could have a price of 1.76 and it would display as 1.7600, or you could have a number of 1.7666 which would display as true 1.7666. You can adjust the round and truncate length if you want more or less 0s to trail. Hope this helps.
{% assign price = 1.765 %}
{% assign price_split = price | round: 4 | split: "." %}
{% assign int = price_split[0] %}
{% assign frac = price_split[1] | append: "0000" | truncate: 4, "" %}
Formatted: {{ int }}.{{ frac }}