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	$29.89	13.159%	$33.8232	$33.82	$33.80	$33.80
Purchase #2	$96.41	7.346%	$103.4923	$103.49	$103.50	$103.50
Purchase #3	$8.81	5.433%	$9.2886	$9.29	$9.30	$9.30
Purchase #4	$220.87	4.802%	$231.4762	$231.48	$231.50	$231.50
Purchase #5	$20.95	8.688%	$22.7701	$22.77	$22.75	$22.80
Purchase #6	$102.71	4.741%	$107.5795	$107.58	$107.60	$107.60
Purchase #7	$151.47	4.570%	$158.3922	$158.39	$158.40	$158.40
7 purchase totals =	$631.11		$666.8221	$666.82	$666.85	$666.90