Fix rounding error with Ruby 2.4
Fix rounding error with Ruby 2.4

Using ruby 2.2, the format used to round automatically, Now with ruby 2.4, it only truncates
```
# using 2.4
(byebug)  (format '%014.2f', amount).gsub('.','')
"0000000200056"
(byebug)  (format '%014.2f', amount.round(2)).gsub('.','')
"0000000200057"
(byebug) 
```
with 2.2, result is same
payrollhero/uob-payroll,payrollhero/uob-payroll