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	$170.73	11.633%	$190.591	$190.59	$190.60	$190.60
Purchase #2	$135.85	11.815%	$151.9007	$151.90	$151.90	$151.90
Purchase #3	$46.54	5.422%	$49.0634	$49.06	$49.05	$49.10
Purchase #4	$34.86	7.135%	$37.3473	$37.35	$37.35	$37.30
Purchase #5	$16.83	12.144%	$18.8738	$18.87	$18.85	$18.90
Purchase #6	$63.95	5.670%	$67.576	$67.58	$67.60	$67.60
Purchase #7	$59.96	8.863%	$65.2743	$65.27	$65.25	$65.30
7 purchase totals =	$528.72		$580.6265	$580.62	$580.60	$580.70