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	$9.36	9.193%	$10.2205	$10.22	$10.20	$10.20
Purchase #2	$50.71	11.139%	$56.3586	$56.36	$56.35	$56.40
Purchase #3	$89.78	10.245%	$98.978	$98.98	$99.00	$99.00
Purchase #4	$80.77	11.763%	$90.271	$90.27	$90.25	$90.30
Purchase #5	$120.42	10.122%	$132.6089	$132.61	$132.60	$132.60
Purchase #6	$245.42	5.710%	$259.4335	$259.43	$259.45	$259.40
Purchase #7	$106.64	4.353%	$111.282	$111.28	$111.30	$111.30
7 purchase totals =	$703.10		$759.1525	$759.15	$759.15	$759.20