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	$14.82	12.770%	$16.7125	$16.71	$16.70	$16.70
Purchase #2	$61.64	7.801%	$66.4485	$66.45	$66.45	$66.40
Purchase #3	$159.56	8.805%	$173.6093	$173.61	$173.60	$173.60
Purchase #4	$151.46	11.569%	$168.9824	$168.98	$169.00	$169.00
Purchase #5	$47.29	10.257%	$52.1405	$52.14	$52.15	$52.10
Purchase #6	$54.49	12.203%	$61.1394	$61.14	$61.15	$61.10
Purchase #7	$51.56	4.519%	$53.89	$53.89	$53.90	$53.90
7 purchase totals =	$540.82		$592.9226	$592.92	$592.95	$592.80