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	$37.32	13.621%	$42.4034	$42.40	$42.40	$42.40
Purchase #2	$55.93	12.758%	$63.0655	$63.07	$63.05	$63.10
Purchase #3	$138.53	10.772%	$153.4525	$153.45	$153.45	$153.50
Purchase #4	$169.79	12.353%	$190.7642	$190.76	$190.75	$190.80
Purchase #5	$58.94	6.186%	$62.586	$62.59	$62.60	$62.60
Purchase #6	$135.49	3.123%	$139.7214	$139.72	$139.70	$139.70
Purchase #7	$152.53	10.243%	$168.1536	$168.15	$168.15	$168.20
7 purchase totals =	$748.53		$820.1466	$820.14	$820.10	$820.30