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	$121.72	12.182%	$136.5479	$136.55	$136.55	$136.50
Purchase #2	$19.62	8.350%	$21.2583	$21.26	$21.25	$21.30
Purchase #3	$176.82	11.305%	$196.8095	$196.81	$196.80	$196.80
Purchase #4	$53.51	4.708%	$56.0293	$56.03	$56.05	$56.00
Purchase #5	$49.63	13.730%	$56.4442	$56.44	$56.45	$56.40
Purchase #6	$47.47	4.486%	$49.5995	$49.60	$49.60	$49.60
Purchase #7	$15.33	3.694%	$15.8963	$15.90	$15.90	$15.90
7 purchase totals =	$484.10		$532.5850	$532.59	$532.60	$532.50