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	$104.64	6.420%	$111.3579	$111.36	$111.35	$111.40
Purchase #2	$72.39	4.207%	$75.4354	$75.44	$75.45	$75.40
Purchase #3	$184.25	8.105%	$199.1835	$199.18	$199.20	$199.20
Purchase #4	$236.90	9.152%	$258.5811	$258.58	$258.60	$258.60
Purchase #5	$151.65	13.130%	$171.5616	$171.56	$171.55	$171.60
Purchase #6	$55.35	13.603%	$62.8793	$62.88	$62.90	$62.90
Purchase #7	$93.49	7.106%	$100.1334	$100.13	$100.15	$100.10
7 purchase totals =	$898.67		$979.1322	$979.13	$979.20	$979.20