Fix bidding with different currencies

Summary

When user places a bid on item with different currency, the form requires the user to put weird value like "10,0036094964385".

Steps to Reproduce

1. Add a new item to the listing.
2. Go to settings and change your preferred currency to different one, that you used when adding the item.
3. Go to the item page of the recently added item and place a bid with normal value, such as "5,50"

Expected Outcome

Bid should be placed successfully, assuming that it wasn't less than minimum bid.

Actual Outcome

The form notifies the user that value is not acceptable, and gives user two closet "acceptable" values that are oddly specific.

Possible fixes

I initially thought that saving prices in database as integers would fix this, but since all values are handled in the user interface as real numbers (like 5,50), issue would still be present when doing currency conversion. The simplest solution may be to round up the minimum bid to the closet tenth, so it aligns with input field's "step" attribute.