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	$153.88	9.466%	$168.4463	$168.45	$168.45	$168.40
Purchase #2	$160.89	3.233%	$166.0916	$166.09	$166.10	$166.10
Purchase #3	$146.38	6.543%	$155.9576	$155.96	$155.95	$156.00
Purchase #4	$177.86	5.436%	$187.5285	$187.53	$187.55	$187.50
Purchase #5	$159.49	7.380%	$171.2604	$171.26	$171.25	$171.30
Purchase #6	$71.81	4.640%	$75.142	$75.14	$75.15	$75.10
Purchase #7	$51.25	6.351%	$54.5049	$54.50	$54.50	$54.50
7 purchase totals =	$921.56		$978.9313	$978.93	$978.95	$978.90