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	$147.70	12.754%	$166.5377	$166.54	$166.55	$166.50
Purchase #2	$105.50	11.490%	$117.622	$117.62	$117.60	$117.60
Purchase #3	$46.55	10.455%	$51.4168	$51.42	$51.40	$51.40
Purchase #4	$43.46	7.527%	$46.7312	$46.73	$46.75	$46.70
Purchase #5	$21.38	5.680%	$22.5944	$22.59	$22.60	$22.60
Purchase #6	$177.28	4.829%	$185.8409	$185.84	$185.85	$185.80
Purchase #7	$39.76	7.606%	$42.7841	$42.78	$42.80	$42.80
7 purchase totals =	$581.63		$633.5271	$633.52	$633.55	$633.40