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	$161.46	4.240%	$168.3059	$168.31	$168.30	$168.30
Purchase #2	$48.43	9.140%	$52.8565	$52.86	$52.85	$52.90
Purchase #3	$228.43	10.395%	$252.1753	$252.18	$252.20	$252.20
Purchase #4	$54.89	12.681%	$61.8506	$61.85	$61.85	$61.90
Purchase #5	$65.93	6.521%	$70.2293	$70.23	$70.25	$70.20
Purchase #6	$65.77	7.642%	$70.7961	$70.80	$70.80	$70.80
Purchase #7	$138.37	3.385%	$143.0538	$143.05	$143.05	$143.10
7 purchase totals =	$763.28		$819.2675	$819.28	$819.30	$819.40