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	$43.41	10.313%	$47.8869	$47.89	$47.90	$47.90
Purchase #2	$172.27	6.525%	$183.5106	$183.51	$183.50	$183.50
Purchase #3	$95.28	4.476%	$99.5447	$99.54	$99.55	$99.50
Purchase #4	$126.27	10.688%	$139.7657	$139.77	$139.75	$139.80
Purchase #5	$238.51	7.169%	$255.6088	$255.61	$255.60	$255.60
Purchase #6	$157.61	7.832%	$169.954	$169.95	$169.95	$170.00
Purchase #7	$28.91	3.356%	$29.8802	$29.88	$29.90	$29.90
7 purchase totals =	$862.26		$926.1509	$926.15	$926.15	$926.20