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	$39.82	9.581%	$43.6352	$43.64	$43.65	$43.60
Purchase #2	$102.64	8.611%	$111.4783	$111.48	$111.50	$111.50
Purchase #3	$31.64	4.244%	$32.9828	$32.98	$33.00	$33.00
Purchase #4	$234.93	9.536%	$257.3329	$257.33	$257.35	$257.30
Purchase #5	$34.81	7.247%	$37.3327	$37.33	$37.35	$37.30
Purchase #6	$118.50	4.764%	$124.1453	$124.15	$124.15	$124.10
Purchase #7	$166.82	10.711%	$184.6881	$184.69	$184.70	$184.70
7 purchase totals =	$729.16		$791.5953	$791.60	$791.70	$791.50