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	$229.58	12.125%	$257.4166	$257.42	$257.40	$257.40
Purchase #2	$49.78	4.164%	$51.8528	$51.85	$51.85	$51.90
Purchase #3	$172.82	13.489%	$196.1317	$196.13	$196.15	$196.10
Purchase #4	$193.47	10.779%	$214.3241	$214.32	$214.30	$214.30
Purchase #5	$130.81	9.613%	$143.3848	$143.38	$143.40	$143.40
Purchase #6	$155.25	11.260%	$172.7312	$172.73	$172.75	$172.70
Purchase #7	$237.25	13.541%	$269.376	$269.38	$269.40	$269.40
7 purchase totals =	$1,168.96		$1,305.2172	$1,305.21	$1,305.25	$1,305.20