Each Store TP+1 increases your TP gain by 1% of normal. For instance, a 450 delay Great Katana normally gets 11.3 TP per hit. With Store TP +10 you get 11.3*1.10 = 12.4 TP per hit. TP gain is always rounded down to the nearest 0.1 TP.
SAM have inherent Store TP.
SAM15: Store TP I = Store TP+10
SAM30: Store TP II = Store TP+15
SAM50: Store TP III = Store TP+20
SAM75: Store TP IV = Store TP+25
The most useful amounts of Store TP are those that will get you to 100 TP in fewer hits. A SAM75 with a 450 delay Great Katana gets 14.1 TP (11.3+25%) per hit; 7 hits make 98.7 TP, not quite enough.
Adding Store TP+2 in equipment or food brings this up to 14.3 (11.3+27%) TP per hit, or 100.1 TP in 7 hits.
Getting down to 6 hits for 100 TP requires a serious focus on Store TP equipment; you need Store TP+23 from gear and food. One way to get this is with Hachiman body, hands, legs, feet and an Attila's Earring. Getting an HQ of any of the Hachiman pieces would allow you to drop the earring.
Other jobs can also use Store TP equipment and food to reduce the number of hits to 100 TP, though their options are more limited. A 504-delay Great Axe such as the Martial Bhuj gives 12.3TP per hit, or 98.4TP per 8 hits. Store TP+2 boosts this to 12.5TP per hit, or 100TP per 8 hits. Rajas Ring would cover this, or Brutal Earring+Attila's Earring, or two Attila's Earrings, or one of the pasta foods.
Store TP+5 from Rajas Ring is also enough to get 100TP in 8 hits from a 480 delay scythe or Great Sword. Store TP+6 (Rajas+Brutal) is enough for a 470 delay weapon. The 528 delay scythes and 444 delay GS don't need any Store TP; they already give just over 100TP in 8 and 9 hits, respectively.