[FIX] base: QWeb monetary field rounding

QWeb monetary widget uses the precision of the currency to know the number of
digits to display on a price. The number of digits is based on log10(rounding).
For currency with rounding different than 10^x (e.g. in Switzerland 0.05
to allow 5 cents coins only), the number of displayed digits should be rounded
up. e.g. log10(0.05) is -1.3, rounded up to 2 digits.

Fixes #3233