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	$12.59	5.253%	$13.2514	$13.25	$13.25	$13.30
Purchase #2	$201.58	10.167%	$222.0746	$222.07	$222.05	$222.10
Purchase #3	$109.66	13.840%	$124.8369	$124.84	$124.85	$124.80
Purchase #4	$106.72	12.842%	$120.425	$120.43	$120.45	$120.40
Purchase #5	$72.87	12.205%	$81.7638	$81.76	$81.75	$81.80
Purchase #6	$146.27	8.459%	$158.643	$158.64	$158.65	$158.60
Purchase #7	$80.60	7.732%	$86.832	$86.83	$86.85	$86.80
7 purchase totals =	$730.29		$807.8267	$807.82	$807.85	$807.80