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	$120.64	9.525%	$132.131	$132.13	$132.15	$132.10
Purchase #2	$143.48	13.439%	$162.7623	$162.76	$162.75	$162.80
Purchase #3	$54.49	4.234%	$56.7971	$56.80	$56.80	$56.80
Purchase #4	$9.43	9.705%	$10.3452	$10.35	$10.35	$10.30
Purchase #5	$12.78	5.120%	$13.4343	$13.43	$13.45	$13.40
Purchase #6	$116.67	12.836%	$131.6458	$131.65	$131.65	$131.60
Purchase #7	$30.52	8.643%	$33.1578	$33.16	$33.15	$33.20
7 purchase totals =	$488.01		$540.2735	$540.28	$540.30	$540.20