I'm having the same issue, using allocate or multiply is resulting in different values than what you suppose to have when trying to resolve the tax amounts.

Example:

const priceAmount = 9700; 
const tax = 21;

const price = dinero({
   amount: priceAmount.value,
   currency: EUR,
});

const multiplied = multiply(priceAmount, { amount: tax, scale: 2 });
const [d1, d2] = allocate(priceAmount, [value, (100 - tax)]); 

toSnapshot(multiplied); //20,37
toSnapshot(d1, d2); //20,37  76,63

Expected result:

const subtotal = priceAmount / 1 + (tax / 100);
const taxAmount = (priceAmount * tax / 100) / tax;

console.log(subtotal); //80,17
console.log(taxAmount); //16,83

How do you save taxes in your DB?

Based on my experience, I always use the 'dinero' for calculations. what I typically do is the following:

• Calculate the scaled tax amount, add 2 to the specified scaling unit (since taxes are saved as a percentage) and sum it by the scaling unit value. For example, if the tax value is 1.553, and your scaling unit is 5 (scaling unit is determined by you, it depends on how decimal numbers you can get for tax e.g. 1.555, 1.1234567, etc..), so the value will be saved in the database as 155300 (here I'm assuming that you saved the tax value in db by fixed scale (scale unit for tax) ). When retrieving the value from the database, the scaled amount will be as follows:

{
  amount: taxValue,
  scale: 5 (fixed scale value for tax) + 2
}

so the value will be 0.01553

• Determine the tax amount by multiplying the total price with the scaled tax amount using the di.multiply function.
• Add the calculated tax amount to the total price using the di.add function to get the final price including taxes.