> No, it's not metaphorical
It is, though largely due to confusion rather than intentional metaphor. (Exception: when described as a “shadow tax,” though that is still a close metaphor and only applies to debt-monetising monetary inflation.)
> If in January, you can buy something for $1, then in February because of inflation it becomes $1.10, that's a 10% tax increase
You’re confusing taxes and costs.
When Russia invaded Ukraine, they didn’t levy a tax on poor Egyptians even though Moscow’s actions raised their food costs. Cost increases are taxing [1]. Confusing something taxing with a tax [2] is a common mistake but still wrong. (And valiantly wrong in a policy context.)