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	$11.87	8.301%	$12.8553	$12.86	$12.85	$12.90
Purchase #2	$241.54	12.257%	$271.1456	$271.15	$271.15	$271.10
Purchase #3	$208.84	11.841%	$233.5687	$233.57	$233.55	$233.60
Purchase #4	$179.31	11.227%	$199.4411	$199.44	$199.45	$199.40
Purchase #5	$170.53	5.428%	$179.7864	$179.79	$179.80	$179.80
Purchase #6	$111.85	13.617%	$127.0806	$127.08	$127.10	$127.10
Purchase #7	$186.93	3.865%	$194.1548	$194.15	$194.15	$194.20
7 purchase totals =	$1,110.87		$1,218.0325	$1,218.04	$1,218.05	$1,218.10