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	$99.92	3.568%	$103.4851	$103.49	$103.50	$103.50
Purchase #2	$201.62	6.455%	$214.6346	$214.63	$214.65	$214.60
Purchase #3	$143.69	10.378%	$158.6021	$158.60	$158.60	$158.60
Purchase #4	$96.70	7.647%	$104.0946	$104.09	$104.10	$104.10
Purchase #5	$82.63	5.363%	$87.0614	$87.06	$87.05	$87.10
Purchase #6	$248.42	4.218%	$258.8984	$258.90	$258.90	$258.90
Purchase #7	$146.61	3.541%	$151.8015	$151.80	$151.80	$151.80
7 purchase totals =	$1,019.59		$1,078.5777	$1,078.57	$1,078.60	$1,078.60