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	$53.88	4.734%	$56.4307	$56.43	$56.45	$56.40
Purchase #2	$95.81	6.795%	$102.3203	$102.32	$102.30	$102.30
Purchase #3	$99.43	4.511%	$103.9153	$103.92	$103.90	$103.90
Purchase #4	$51.85	3.625%	$53.7296	$53.73	$53.75	$53.70
Purchase #5	$61.93	5.612%	$65.4055	$65.41	$65.40	$65.40
Purchase #6	$155.50	11.628%	$173.5815	$173.58	$173.60	$173.60
Purchase #7	$20.93	12.141%	$23.4711	$23.47	$23.45	$23.50
7 purchase totals =	$539.33		$578.8540	$578.86	$578.85	$578.80