meta_query: using BETWEEN with floats and/or casting to DECIMAL

You can filter generated SQL and add precision parameters that you need.

Enable filters for get_posts() by adding following to query:

'suppress_filters' => false,

And:

add_filter('posts_where','cast_decimal_precision');

function cast_decimal_precision( $where ) {

    return str_replace('DECIMAL','DECIMAL(10,3)',$where);
}

Update

With Jan’s suggestion:

add_filter('get_meta_sql','cast_decimal_precision');

function cast_decimal_precision( $array ) {

    $array['where'] = str_replace('DECIMAL','DECIMAL(10,3)',$array['where']);

    return $array;
}