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	$80.31	11.624%	$89.6452	$89.65	$89.65	$89.60
Purchase #2	$100.72	5.497%	$106.2566	$106.26	$106.25	$106.30
Purchase #3	$60.66	6.209%	$64.4264	$64.43	$64.45	$64.40
Purchase #4	$63.55	3.527%	$65.7914	$65.79	$65.80	$65.80
Purchase #5	$209.53	5.410%	$220.8656	$220.87	$220.85	$220.90
Purchase #6	$46.35	10.218%	$51.086	$51.09	$51.10	$51.10
Purchase #7	$160.54	11.394%	$178.8319	$178.83	$178.85	$178.80
7 purchase totals =	$721.66		$776.9031	$776.92	$776.95	$776.90