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	$48.36	4.454%	$50.514	$50.51	$50.50	$50.50
Purchase #2	$75.82	12.716%	$85.4613	$85.46	$85.45	$85.50
Purchase #3	$140.60	13.190%	$159.1451	$159.15	$159.15	$159.10
Purchase #4	$138.82	10.406%	$153.2656	$153.27	$153.25	$153.30
Purchase #5	$166.73	3.767%	$173.0107	$173.01	$173.00	$173.00
Purchase #6	$65.75	3.519%	$68.0637	$68.06	$68.05	$68.10
Purchase #7	$91.45	8.635%	$99.3467	$99.35	$99.35	$99.30
7 purchase totals =	$727.53		$788.8071	$788.81	$788.75	$788.80