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	$51.25	6.532%	$54.5977	$54.60	$54.60	$54.60
Purchase #2	$19.69	10.126%	$21.6838	$21.68	$21.70	$21.70
Purchase #3	$214.75	6.297%	$228.2728	$228.27	$228.25	$228.30
Purchase #4	$50.46	8.516%	$54.7572	$54.76	$54.75	$54.80
Purchase #5	$174.74	8.824%	$190.1591	$190.16	$190.15	$190.20
Purchase #6	$19.55	6.715%	$20.8628	$20.86	$20.85	$20.90
Purchase #7	$28.85	10.670%	$31.9283	$31.93	$31.95	$31.90
7 purchase totals =	$559.29		$602.2617	$602.26	$602.25	$602.40