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	$5.55	11.156%	$6.1692	$6.17	$6.15	$6.20
Purchase #2	$102.65	9.599%	$112.5034	$112.50	$112.50	$112.50
Purchase #3	$168.26	4.360%	$175.5961	$175.60	$175.60	$175.60
Purchase #4	$220.60	13.522%	$250.4295	$250.43	$250.45	$250.40
Purchase #5	$111.33	5.392%	$117.3329	$117.33	$117.35	$117.30
Purchase #6	$102.89	8.669%	$111.8095	$111.81	$111.80	$111.80
Purchase #7	$154.74	8.347%	$167.6561	$167.66	$167.65	$167.70
7 purchase totals =	$866.02		$941.4967	$941.50	$941.50	$941.50