[IMP] account: use float_compare for taxes

Avoiding some python float representation errors
Revert "[FIX] product,float_utils: perform ceiling via float_round with new rounding_method UP"

This reverts commit d4972ffdb6b9356a524eef1dbc11f455ff4473f2.

Seems to break some cases, at least in _product_reserve from stock/stock.py

Actual use case:

SELECT product_uom, sum(product_qty) AS product_qty FROM stock_move WHERE location_dest_id=%s AND location_id<>%s AND product_id=3645 AND state='done' GROUP BY product_uom;
returning 1 | 6

SELECT product_uom,-sum(product_qty) AS product_qty FROM stock_move WHERE location_id=%s AND location_dest_id<>%s AND product_id=%s AND state in ('done', 'assigned') GROUP BY product_uom;
returning 1 | -6

results += cr.dictfetchall()
    total = 0.0
    results2 = 0.0
    for r in results:
        amount = uom_obj._compute_qty(cr, uid, r['product_uom'], r['product_qty'], context.get('uom', False))
        results2 += amount
        total += amount
Total = 1, amount = -5

It should actually be
Total = 0, amount = -6
[MERGE] forward port of branch 7.0 up to 333852e