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	$41.44	4.428%	$43.275	$43.28	$43.30	$43.30
Purchase #2	$109.62	7.198%	$117.5104	$117.51	$117.50	$117.50
Purchase #3	$53.33	5.505%	$56.2658	$56.27	$56.25	$56.30
Purchase #4	$59.93	6.846%	$64.0328	$64.03	$64.05	$64.00
Purchase #5	$229.32	3.265%	$236.8073	$236.81	$236.80	$236.80
Purchase #6	$103.33	8.321%	$111.9281	$111.93	$111.95	$111.90
Purchase #7	$43.87	10.211%	$48.3496	$48.35	$48.35	$48.30
7 purchase totals =	$640.84		$678.1690	$678.18	$678.20	$678.10