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	$46.50	8.382%	$50.3976	$50.40	$50.40	$50.40
Purchase #2	$131.49	11.502%	$146.614	$146.61	$146.60	$146.60
Purchase #3	$147.35	7.541%	$158.4617	$158.46	$158.45	$158.50
Purchase #4	$249.86	9.422%	$273.4018	$273.40	$273.40	$273.40
Purchase #5	$222.62	9.549%	$243.878	$243.88	$243.90	$243.90
Purchase #6	$15.51	13.607%	$17.6204	$17.62	$17.60	$17.60
Purchase #7	$40.95	4.333%	$42.7244	$42.72	$42.70	$42.70
7 purchase totals =	$854.28		$933.0979	$933.09	$933.05	$933.10