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	$168.36	9.323%	$184.0562	$184.06	$184.05	$184.10
Purchase #2	$127.30	11.172%	$141.522	$141.52	$141.50	$141.50
Purchase #3	$83.89	4.625%	$87.7699	$87.77	$87.75	$87.80
Purchase #4	$61.85	12.243%	$69.4223	$69.42	$69.40	$69.40
Purchase #5	$200.45	10.178%	$220.8518	$220.85	$220.85	$220.90
Purchase #6	$60.54	9.663%	$66.39	$66.39	$66.40	$66.40
Purchase #7	$54.86	4.244%	$57.1883	$57.19	$57.20	$57.20
7 purchase totals =	$757.25		$827.2005	$827.20	$827.15	$827.30