Hi Hannah. Yes, I can confirm that all taxes have 4 decimal places.
Also for comparison, I also did another test using the same numbers but a different destination that is only subject to 1 of the taxes and the result was proper calculations:
Subtotal: $1.99
Shipping: $8.50
5% GST : $0.52
TOTAL : $11.01
Subtotal: $1.9900
Shipping: $8.5000
5% GST : $0.5245
TOTAL : $11.0145