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	$97.90	13.205%	$110.8277	$110.83	$110.85	$110.80
Purchase #2	$39.78	6.388%	$42.3211	$42.32	$42.30	$42.30
Purchase #3	$103.67	8.660%	$112.6478	$112.65	$112.65	$112.60
Purchase #4	$169.76	8.370%	$183.9689	$183.97	$183.95	$184.00
Purchase #5	$50.80	6.108%	$53.9029	$53.90	$53.90	$53.90
Purchase #6	$34.78	11.190%	$38.6719	$38.67	$38.65	$38.70
Purchase #7	$86.30	3.284%	$89.1341	$89.13	$89.15	$89.10
7 purchase totals =	$582.99		$631.4744	$631.47	$631.45	$631.40