[Refunds] Update networking layer to support multiple tax rates

[hichamboushaba]

Closes: WOOMOB-394

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• I have considered if this change warrants release notes and have added them to RELEASE-NOTES.txt if necessary. Use the "[Internal]" label for non-user-facing changes.

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[dangermattic]

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce-Wear Android by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce-Wear Android
	Platform	⌚️ Wear OS
	Flavor	Jalapeno
	Build Type	Debug
	Commit	0de75f6
	Direct Download	woocommerce-wear-prototype-build-pr14002-0de75f6.apk

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce Android by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce Android
	Platform	📱 Mobile
	Flavor	Jalapeno
	Build Type	Debug
	Commit	0de75f6
	Direct Download	woocommerce-prototype-build-pr14002-0de75f6.apk