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	$147.61	7.809%	$159.1369	$159.14	$159.15	$159.10
Purchase #2	$50.48	13.615%	$57.3529	$57.35	$57.35	$57.40
Purchase #3	$23.91	7.449%	$25.6911	$25.69	$25.70	$25.70
Purchase #4	$53.71	10.563%	$59.3834	$59.38	$59.40	$59.40
Purchase #5	$151.31	4.298%	$157.8133	$157.81	$157.80	$157.80
Purchase #6	$153.48	13.168%	$173.6902	$173.69	$173.70	$173.70
Purchase #7	$134.92	9.312%	$147.4838	$147.48	$147.50	$147.50
7 purchase totals =	$715.42		$780.5516	$780.54	$780.60	$780.60