If you're just using PTC and drawing pixels, then it's just a case of repeating each source pixel many times.
You might have
for y=0 to srcy-1
for x=0 to srcx-1
pix = srcgfx[x+y*srcx]
for h=0 to yscale-1
for w=0 to xscale-1
screen[dstx+w+(dsty+h)*SCREENWIDTH]=pix
next
next
dstx += xscale
next
dstx -= srcx*xscale
dsty += yscale
next
Where xscale and yscale are the x and y repeat counts, so you might want 8 and 8 for a 64x64 graphic, and dstx, dsty are the screen position of the sprite, scrx and srcy are the source size (8,8), and SCREENWIDTH is the screen width.
(Code untested)
Jim