Depends on how much you have in your bank account and how many other tiers you have other than the investment category...
If your transactions are consistently more than $5000 and you have one other tier, e.g. credit card, you would get a 0.3% increase in interest rate. Is this 0.3% increase more than the decrease you'd incur by placing $3000 in SSB versus leaving in your DBS Multiplier account?
Suppose your transactions are between $5000 and $15000. Then your interest rate would jump from 1.9% to 2.2%. Assuming the SSB interest rate is 1.9% (for six months - is this realistic?), it would seem worth it.
Some other points to consider though:
1) The SSB interest rate is step-up, so you get lower interest rates at the start and higher interest rates at the end that average out to get your headline figure. If DBS were to change the Multiplier scheme without warning, it might not be worth it.
2) There is a transaction fee of $2 per bid you put, i.e. $12 for six bids. You have to add this $12 loss to the decrease in interest you'd incur on the $3000.
3) Mental load. It's troublesome to do all this. Suppose you had $50000 in your account, transactions between $5000 and $15000, and you only had the salary credit and two categories. Your 0.3% increase in interest translates to an increase of $150 per year...without considering the other cons. However, if your transactions were more than $15000 consistently, you get a 1.42% increase, which translates to an increase of $710 per year. Is this realistic though?
