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	$30.76	11.351%	$34.2516	$34.25	$34.25	$34.30
Purchase #2	$83.75	11.183%	$93.1158	$93.12	$93.10	$93.10
Purchase #3	$34.56	7.314%	$37.0877	$37.09	$37.10	$37.10
Purchase #4	$122.84	3.700%	$127.3851	$127.39	$127.40	$127.40
Purchase #5	$95.79	3.490%	$99.1331	$99.13	$99.15	$99.10
Purchase #6	$63.52	4.853%	$66.6026	$66.60	$66.60	$66.60
Purchase #7	$83.58	13.434%	$94.8081	$94.81	$94.80	$94.80
7 purchase totals =	$514.80		$552.3840	$552.39	$552.40	$552.40