SELECT 
  destination_id, 
  rate_value, 
  rate_type 
FROM 
  cscart_tax_rates 
WHERE 
  tax_id = 6 
  AND destination_id = 9

Query time 0.00017

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_tax_rates const tax_rate tax_rate 6 const,const 1

Result

destination_id rate_value rate_type
9 19.000 P