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	$40.90	6.298%	$43.4759	$43.48	$43.50	$43.50
Purchase #2	$246.42	10.105%	$271.3207	$271.32	$271.30	$271.30
Purchase #3	$202.73	9.296%	$221.5758	$221.58	$221.60	$221.60
Purchase #4	$66.68	8.389%	$72.2738	$72.27	$72.25	$72.30
Purchase #5	$106.46	4.343%	$111.0836	$111.08	$111.10	$111.10
Purchase #6	$199.27	5.791%	$210.8097	$210.81	$210.80	$210.80
Purchase #7	$153.32	9.140%	$167.3334	$167.33	$167.35	$167.30
7 purchase totals =	$1,015.78		$1,097.8729	$1,097.87	$1,097.90	$1,097.90