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	$176.51	3.688%	$183.0197	$183.02	$183.00	$183.00
Purchase #2	$51.58	8.406%	$55.9158	$55.92	$55.90	$55.90
Purchase #3	$44.87	13.153%	$50.7718	$50.77	$50.75	$50.80
Purchase #4	$120.80	8.320%	$130.8506	$130.85	$130.85	$130.90
Purchase #5	$81.47	10.406%	$89.9478	$89.95	$89.95	$89.90
Purchase #6	$18.86	13.574%	$21.4201	$21.42	$21.40	$21.40
Purchase #7	$233.80	6.529%	$249.0648	$249.06	$249.05	$249.10
7 purchase totals =	$727.89		$780.9906	$780.99	$780.90	$781.00