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	$77.85	7.114%	$83.3882	$83.39	$83.40	$83.40
Purchase #2	$49.70	9.191%	$54.2679	$54.27	$54.25	$54.30
Purchase #3	$74.73	11.867%	$83.5982	$83.60	$83.60	$83.60
Purchase #4	$112.90	13.807%	$128.4881	$128.49	$128.50	$128.50
Purchase #5	$220.62	12.378%	$247.9283	$247.93	$247.95	$247.90
Purchase #6	$152.55	13.753%	$173.5302	$173.53	$173.55	$173.50
Purchase #7	$100.53	12.244%	$112.8389	$112.84	$112.85	$112.80
7 purchase totals =	$788.88		$884.0398	$884.05	$884.10	$884.00