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	$7.28	4.344%	$7.5962	$7.60	$7.60	$7.60
Purchase #2	$242.92	11.773%	$271.519	$271.52	$271.50	$271.50
Purchase #3	$21.69	4.383%	$22.6407	$22.64	$22.65	$22.60
Purchase #4	$151.89	3.244%	$156.8173	$156.82	$156.80	$156.80
Purchase #5	$237.51	10.365%	$262.1279	$262.13	$262.15	$262.10
Purchase #6	$101.64	10.462%	$112.2736	$112.27	$112.25	$112.30
Purchase #7	$206.75	12.850%	$233.3174	$233.32	$233.30	$233.30
7 purchase totals =	$969.68		$1,066.2921	$1,066.30	$1,066.25	$1,066.20