When a retailer routinely prices goods at $$9\mathrm{.}97$ and $$7\mathrm{.}36$ rather than $$10\mathrm{.}00$ and $$7\mathrm{.}50,$ the retailer is using:

a$.$

variable pricing.

b$.$

penetration pricing.

c$.$

odd pricing.

d$.$

none of the above