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	$54.58	11.106%	$60.6417	$60.64	$60.65	$60.60
Purchase #2	$196.97	9.582%	$215.8437	$215.84	$215.85	$215.80
Purchase #3	$139.90	10.810%	$155.0232	$155.02	$155.00	$155.00
Purchase #4	$162.85	12.487%	$183.1851	$183.19	$183.20	$183.20
Purchase #5	$50.94	6.697%	$54.3515	$54.35	$54.35	$54.40
Purchase #6	$95.97	9.797%	$105.3722	$105.37	$105.35	$105.40
Purchase #7	$87.51	3.589%	$90.6507	$90.65	$90.65	$90.70
7 purchase totals =	$788.72		$865.0681	$865.06	$865.05	$865.10