How is money storage best implemented in a system?

To store monetary funds in the system, it is better to use integer data types representing the minimal units of currency (for example, kopecks or cents) to avoid rounding errors associated with floating-point.

For example, instead of storing the amount as float64 (123.45), store it as int64 (12345 kopecks).

In Go, this might look like:

// Amount in kopecks
var amount int64 = 12345 // 123.45 rubles

// Conversion to rubles for display
func formatAmount(amount int64) string {
    rub := amount / 100
    kop := amount % 100
    return fmt.Sprintf("%d.%02d", rub, kop)
}

It is also important to use database transactions for atomic operations with monetary funds and to ensure data integrity (for example, through constraints and checks).