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	$155.26	9.773%	$170.4336	$170.43	$170.45	$170.40
Purchase #2	$63.58	11.806%	$71.0863	$71.09	$71.10	$71.10
Purchase #3	$35.58	5.489%	$37.533	$37.53	$37.55	$37.50
Purchase #4	$98.30	13.853%	$111.9175	$111.92	$111.90	$111.90
Purchase #5	$92.88	13.611%	$105.5219	$105.52	$105.50	$105.50
Purchase #6	$120.25	10.671%	$133.0819	$133.08	$133.10	$133.10
Purchase #7	$105.93	11.635%	$118.255	$118.26	$118.25	$118.30
7 purchase totals =	$671.78		$747.8292	$747.83	$747.85	$747.80