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	$188.55	12.787%	$212.6599	$212.66	$212.65	$212.70
Purchase #2	$143.25	10.388%	$158.1308	$158.13	$158.15	$158.10
Purchase #3	$49.82	8.429%	$54.0193	$54.02	$54.00	$54.00
Purchase #4	$97.37	12.395%	$109.439	$109.44	$109.45	$109.40
Purchase #5	$60.36	11.740%	$67.4463	$67.45	$67.45	$67.40
Purchase #6	$34.46	11.370%	$38.3781	$38.38	$38.40	$38.40
Purchase #7	$6.25	5.332%	$6.5833	$6.58	$6.60	$6.60
7 purchase totals =	$580.06		$646.6567	$646.66	$646.70	$646.60