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	$75.95	3.545%	$78.6424	$78.64	$78.65	$78.60
Purchase #2	$185.45	10.846%	$205.5639	$205.56	$205.55	$205.60
Purchase #3	$158.76	9.553%	$173.9263	$173.93	$173.95	$173.90
Purchase #4	$112.49	5.443%	$118.6128	$118.61	$118.60	$118.60
Purchase #5	$5.97	12.531%	$6.7181	$6.72	$6.70	$6.70
Purchase #6	$148.39	7.441%	$159.4317	$159.43	$159.45	$159.40
Purchase #7	$76.39	8.425%	$82.8259	$82.83	$82.85	$82.80
7 purchase totals =	$763.40		$825.7211	$825.72	$825.75	$825.60