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	$130.64	9.585%	$143.1618	$143.16	$143.15	$143.20
Purchase #2	$56.92	4.268%	$59.3493	$59.35	$59.35	$59.30
Purchase #3	$152.27	11.429%	$169.6729	$169.67	$169.65	$169.70
Purchase #4	$140.33	10.868%	$155.5811	$155.58	$155.60	$155.60
Purchase #5	$166.95	6.631%	$178.0205	$178.02	$178.00	$178.00
Purchase #6	$5.83	5.547%	$6.1534	$6.15	$6.15	$6.20
Purchase #7	$82.67	4.846%	$86.6762	$86.68	$86.70	$86.70
7 purchase totals =	$735.61		$798.6152	$798.61	$798.60	$798.70