Formula for Tiered Sales Commission

Ok my problem is this but:
Sales Commissions paid on a tiered structure
`Sales 0 - 1,250,000 = NO Commission Paid
`Sales 1,251,000 - 1,500,000 = 4% of the amount over 1,250,000 (so if sales were 1,400,000, commission would be 6000)
`Sales 1,501,000 - 1,750,000 = 5% of the amount over 1,500,000 and 4% of the full 250,000 from above (so if sales were 1,600,000, commission would be 10000+5000=15000)
and so on with the follow 2 tiers as well
`Sales 1,751,000 - 2,000,000 = 6% of the amount over 1,750,000 and 5% of the full 250,000 from above and 4% of the full 250,000 above that.
`Sales 2,000,000 and above = 7% of any amount over 2,000,000 and 6% of the full 250,000 above and 5% of the full 250,000 from above that and 4% of the full 250,000 above that.

I really hope this makes sense, it has been done manually bu could REALLY use a formula to save a lot of time.

I have manually done the formulas per cell but I would like to do one that can be copied to all others so if any part changes either the tier or % I only have to update in one place.
Total Sales - $1,680,000
End Result (Commission Paid) - $19,000
Formula Used - =(250000*0.04) + ((M16-1500000)*0.05)
M16 is the total sales amount

I am happy to give more examples if needed.

Oh my!!!! Thank you so much, you have made my life so much easier!! Now I can make changes to the tiers or % or sales on the fly to get instant new numbers for the 10 years!! Amazing.