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	$40.37	4.138%	$42.0405	$42.04	$42.05	$42.00
Purchase #2	$81.53	6.798%	$87.0724	$87.07	$87.05	$87.10
Purchase #3	$106.69	11.413%	$118.8665	$118.87	$118.85	$118.90
Purchase #4	$230.76	4.670%	$241.5365	$241.54	$241.55	$241.50
Purchase #5	$48.30	12.116%	$54.152	$54.15	$54.15	$54.20
Purchase #6	$236.71	10.799%	$262.2723	$262.27	$262.25	$262.30
Purchase #7	$88.26	3.734%	$91.5556	$91.56	$91.55	$91.60
7 purchase totals =	$832.62		$897.4958	$897.50	$897.45	$897.60