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	$160.46	11.422%	$178.7877	$178.79	$178.80	$178.80
Purchase #2	$177.52	12.398%	$199.5289	$199.53	$199.55	$199.50
Purchase #3	$41.32	8.167%	$44.6946	$44.69	$44.70	$44.70
Purchase #4	$179.25	3.450%	$185.4341	$185.43	$185.45	$185.40
Purchase #5	$224.25	10.348%	$247.4554	$247.46	$247.45	$247.50
Purchase #6	$20.48	3.726%	$21.2431	$21.24	$21.25	$21.20
Purchase #7	$79.28	13.413%	$89.9138	$89.91	$89.90	$89.90
7 purchase totals =	$882.56		$967.0576	$967.05	$967.10	$967.00