Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.52	8.781%	$96.2929	$96.29	$96.30	$96.30
Purchase #2	$172.63	12.505%	$194.2174	$194.22	$194.20	$194.20
Purchase #3	$51.66	10.778%	$57.2279	$57.23	$57.25	$57.20
Purchase #4	$43.84	4.503%	$45.8141	$45.81	$45.80	$45.80
Purchase #5	$162.59	11.204%	$180.8066	$180.81	$180.80	$180.80
Purchase #6	$63.25	4.599%	$66.1589	$66.16	$66.15	$66.20
Purchase #7	$96.44	7.747%	$103.9112	$103.91	$103.90	$103.90
7 purchase totals =	$678.93		$744.4290	$744.43	$744.40	$744.40