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	$232.48	4.476%	$242.8858	$242.89	$242.90	$242.90
Purchase #2	$149.33	3.226%	$154.1474	$154.15	$154.15	$154.10
Purchase #3	$64.26	11.446%	$71.6152	$71.62	$71.60	$71.60
Purchase #4	$115.91	6.856%	$123.8568	$123.86	$123.85	$123.90
Purchase #5	$101.60	10.273%	$112.0374	$112.04	$112.05	$112.00
Purchase #6	$19.32	8.338%	$20.9309	$20.93	$20.95	$20.90
Purchase #7	$105.49	6.635%	$112.4893	$112.49	$112.50	$112.50
7 purchase totals =	$788.39		$837.9628	$837.98	$838.00	$837.90