SQL Server 2019

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with t as (/*select 1 schet_factura,1 id,0 amount,1000 nds union all*/
           select 1 schet_factura,1 id,27.38 amount,1000 nds union all
           select 1,6,59.01,1000 union all
           select 1,5,99.99,1000 union all 
           select 1,2,99.99,1000 union all 
           select 1,3,99.99,1000 union all 
           select 1,4,99.99,1000 union all
           select 1,7,null,1000 
          )
, x as
(select t.schet_factura
      , t.id
      , t.amount n_amount
      , s.amount
      , t.nds
      , iif(s.amount = 0, 0, round(t.nds * s.amount / sum(s.amount) over(partition by t.schet_factura), 2)) d_nds
   from t
  cross apply(values(isnull(amount, 0))) s(amount))

, y as
(select x.schet_factura
      , x.id
      , x.n_amount
      , x.amount
      , x.nds
      , x.d_nds
      , iif(x.id = last_value(x.id) over(partition by x.schet_factura order by x.amount, x.id rows between current row and unbounded following)
            /*and sum(x.d_nds) over(partition by schet_factura) > 0*/ /*be or not to be*/
          , x.nds - sum(x.d_nds) over(partition by schet_factura)
          , 0) d_nds_round_fix
   from x)
  
select y.schet_factura
     , y.id
     , y.n_amount
     , y.amount
     , y.nds
     , convert(decimal(18, 2), y.d_nds) d_nds
     , convert(decimal(18, 2), y.d_nds_round_fix) d_nds_round_fix
     , convert(decimal(18, 2), y.d_nds + y.d_nds_round_fix) d_dns_res
     , convert(decimal(18, 2), sum(y.d_nds + y.d_nds_round_fix) over(partition by y.schet_factura)) sum_d_dns_res
  from y
 order by y.schet_factura, y.amount, y.id

schet_factura	id	n_amount	amount	nds	d_nds	d_nds_round_fix	d_dns_res	sum_d_dns_res
1	7	null	0.00	1000	0.00	0.00	0.00	1000.00
1	1	27.38	27.38	1000	56.30	0.00	56.30	1000.00
1	6	59.01	59.01	1000	121.33	0.00	121.33	1000.00
1	2	99.99	99.99	1000	205.59	0.00	205.59	1000.00
1	3	99.99	99.99	1000	205.59	0.00	205.59	1000.00
1	4	99.99	99.99	1000	205.59	0.00	205.59	1000.00
1	5	99.99	99.99	1000	205.59	0.01	205.60	1000.00

with t as (select 1 schet_factura,1 id,0 amount,1000 nds union all
           select 1,7,null,1000 
          )
, x as
(select t.schet_factura
      , t.id
      , t.amount n_amount
      , s.amount
      , t.nds
      , iif(s.amount = 0, 0, round(t.nds * s.amount / sum(s.amount) over(partition by t.schet_factura), 2)) d_nds
   from t
  cross apply(values(isnull(amount, 0))) s(amount))

schet_factura	id	n_amount	amount	nds	d_nds	d_nds_round_fix	d_dns_res	sum_d_dns_res
1	1	0	0	1000	0.00	0.00	0.00	1000.00
1	7	null	0	1000	0.00	1000.00	1000.00	1000.00