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	$44.91	10.259%	$49.5173	$49.52	$49.50	$49.50
Purchase #2	$236.29	8.120%	$255.4767	$255.48	$255.50	$255.50
Purchase #3	$71.32	6.537%	$75.9822	$75.98	$76.00	$76.00
Purchase #4	$92.30	12.382%	$103.7286	$103.73	$103.75	$103.70
Purchase #5	$24.79	4.115%	$25.8101	$25.81	$25.80	$25.80
Purchase #6	$57.30	9.701%	$62.8587	$62.86	$62.85	$62.90
Purchase #7	$99.56	11.860%	$111.3678	$111.37	$111.35	$111.40
7 purchase totals =	$626.47		$684.7414	$684.75	$684.75	$684.80