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	$143.44	8.674%	$155.882	$155.88	$155.90	$155.90
Purchase #2	$155.44	5.548%	$164.0638	$164.06	$164.05	$164.10
Purchase #3	$72.67	10.667%	$80.4217	$80.42	$80.40	$80.40
Purchase #4	$69.80	11.341%	$77.716	$77.72	$77.70	$77.70
Purchase #5	$160.39	4.625%	$167.808	$167.81	$167.80	$167.80
Purchase #6	$146.72	3.304%	$151.5676	$151.57	$151.55	$151.60
Purchase #7	$169.83	7.848%	$183.1583	$183.16	$183.15	$183.20
7 purchase totals =	$918.29		$980.6174	$980.62	$980.55	$980.70