It seems to me that you need to wait for X amount of time with no pulses before you can use the count. As it is your using coinsValue straight away on the first pulse when there may be more pulses on the way, then you delay(1000) which presumably misses all subsequent pulses.
Also you never reset coinsValue so it's value will continue to rise well past 10.
As it stands I would expect the LEDs to light on the 1st, 5th and 10th coins then never again.
coinsChange should be volatile.
There's no reason to have coinsValue as a float, that's silly. Use an int.
Rob