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	$142.34	9.357%	$155.6588	$155.66	$155.65	$155.70
Purchase #2	$22.61	12.513%	$25.4392	$25.44	$25.45	$25.40
Purchase #3	$105.60	8.798%	$114.8907	$114.89	$114.90	$114.90
Purchase #4	$53.93	5.491%	$56.8913	$56.89	$56.90	$56.90
Purchase #5	$90.97	9.647%	$99.7459	$99.75	$99.75	$99.70
Purchase #6	$99.43	9.125%	$108.503	$108.50	$108.50	$108.50
Purchase #7	$74.60	8.278%	$80.7754	$80.78	$80.80	$80.80
7 purchase totals =	$589.48		$641.9043	$641.91	$641.95	$641.90