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	$152.34	13.153%	$172.3773	$172.38	$172.40	$172.40
Purchase #2	$226.45	6.602%	$241.4002	$241.40	$241.40	$241.40
Purchase #3	$29.72	13.241%	$33.6552	$33.66	$33.65	$33.70
Purchase #4	$86.82	11.571%	$96.8659	$96.87	$96.85	$96.90
Purchase #5	$89.93	11.807%	$100.548	$100.55	$100.55	$100.50
Purchase #6	$232.56	12.651%	$261.9812	$261.98	$262.00	$262.00
Purchase #7	$52.40	8.283%	$56.7403	$56.74	$56.75	$56.70
7 purchase totals =	$870.22		$963.5681	$963.58	$963.60	$963.60