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	$15.54	9.591%	$17.0304	$17.03	$17.05	$17.00
Purchase #2	$132.40	5.445%	$139.6092	$139.61	$139.60	$139.60
Purchase #3	$146.90	6.141%	$155.9211	$155.92	$155.90	$155.90
Purchase #4	$172.77	6.550%	$184.0864	$184.09	$184.10	$184.10
Purchase #5	$91.36	10.472%	$100.9272	$100.93	$100.95	$100.90
Purchase #6	$19.97	9.864%	$21.9398	$21.94	$21.95	$21.90
Purchase #7	$91.56	8.793%	$99.6109	$99.61	$99.60	$99.60
7 purchase totals =	$670.50		$719.1250	$719.13	$719.15	$719.00