You can use the special -xls-format to set the format:
<table>
<tr>
<td style="-xls-format:currency_dollar">1000</td>
<td style="-xls-format:currency_pound">1000</td>
</tr>
<tr>
<td style="-xls-format:float">100.012</td>
<td style="-xls-format:date_format1">08/23/17</td>
</tr>
</table>
Numbers & Text Options
default
text
integer
float
percent float
percent integer
accounting float
accounting integer
accounting red float
accounting red integer
exponential
fraction_one_digit
fraction_two_digits
thousands_float
thousands_integer
Currency Options
currency_dollar
currency_euro_prefix
currency_float_euro_prefix
currency_euro_suffix
currency_japanese_yen
currency_pound
Dates & Times Options
date_format1 (m/d/yy)
date_format2 (d-mmm-yy)
date_format3 (d-mmm)
date_format4 (mmm-yy)
date_format5 (h:mm AM/PM)
date_format6 (h:mm:ss AM/PM)
date_format7 (h:mm)
date_format8 (h:mm:ss)
date_format9 (m/d/yy h:mm)
date_format10 (d/m/yy)
date_format11 (d/m/yy h:mm:ss) (xlsx-only)
date_format12 (dd.MM.yyyy) (xlsx-only)
Note: If you use a number format on a text or date cell, the results may be unpredictable.