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	$10.92	13.245%	$12.3664	$12.37	$12.35	$12.40
Purchase #2	$158.97	10.356%	$175.4329	$175.43	$175.45	$175.40
Purchase #3	$154.26	3.628%	$159.8566	$159.86	$159.85	$159.90
Purchase #4	$160.64	4.125%	$167.2664	$167.27	$167.25	$167.30
Purchase #5	$133.51	7.759%	$143.869	$143.87	$143.85	$143.90
Purchase #6	$101.89	3.419%	$105.3736	$105.37	$105.35	$105.40
Purchase #7	$117.86	9.337%	$128.8646	$128.86	$128.85	$128.90
7 purchase totals =	$838.05		$893.0295	$893.03	$892.95	$893.20