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	$89.47	11.873%	$100.0928	$100.09	$100.10	$100.10
Purchase #2	$58.71	5.431%	$61.8985	$61.90	$61.90	$61.90
Purchase #3	$26.76	5.296%	$28.1772	$28.18	$28.20	$28.20
Purchase #4	$109.60	13.126%	$123.9861	$123.99	$124.00	$124.00
Purchase #5	$18.75	11.182%	$20.8466	$20.85	$20.85	$20.80
Purchase #6	$14.95	4.851%	$15.6752	$15.68	$15.70	$15.70
Purchase #7	$57.61	8.623%	$62.5777	$62.58	$62.60	$62.60
7 purchase totals =	$375.85		$413.2541	$413.27	$413.35	$413.30