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	$152.50	4.346%	$159.1277	$159.13	$159.15	$159.10
Purchase #2	$66.51	13.703%	$75.6239	$75.62	$75.60	$75.60
Purchase #3	$25.33	6.816%	$27.0565	$27.06	$27.05	$27.10
Purchase #4	$14.54	6.250%	$15.4488	$15.45	$15.45	$15.40
Purchase #5	$243.41	5.386%	$256.5201	$256.52	$256.50	$256.50
Purchase #6	$13.95	13.355%	$15.813	$15.81	$15.80	$15.80
Purchase #7	$40.85	3.746%	$42.3802	$42.38	$42.40	$42.40
7 purchase totals =	$557.09		$591.9702	$591.97	$591.95	$591.90