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	$29.31	4.576%	$30.6512	$30.65	$30.65	$30.70
Purchase #2	$139.72	4.662%	$146.2337	$146.23	$146.25	$146.20
Purchase #3	$244.52	13.504%	$277.54	$277.54	$277.55	$277.50
Purchase #4	$101.91	10.670%	$112.7838	$112.78	$112.80	$112.80
Purchase #5	$123.61	5.357%	$130.2318	$130.23	$130.25	$130.20
Purchase #6	$208.77	9.367%	$228.3255	$228.33	$228.35	$228.30
Purchase #7	$111.33	4.610%	$116.4623	$116.46	$116.45	$116.50
7 purchase totals =	$959.17		$1,042.2283	$1,042.22	$1,042.30	$1,042.20