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	$229.72	8.639%	$249.5655	$249.57	$249.55	$249.60
Purchase #2	$126.62	12.813%	$142.8438	$142.84	$142.85	$142.80
Purchase #3	$235.27	9.178%	$256.8631	$256.86	$256.85	$256.90
Purchase #4	$183.79	11.286%	$204.5325	$204.53	$204.55	$204.50
Purchase #5	$189.69	4.191%	$197.6399	$197.64	$197.65	$197.60
Purchase #6	$104.28	6.836%	$111.4086	$111.41	$111.40	$111.40
Purchase #7	$103.48	13.366%	$117.3111	$117.31	$117.30	$117.30
7 purchase totals =	$1,172.85		$1,280.1645	$1,280.16	$1,280.15	$1,280.10