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	$161.94	5.213%	$170.3819	$170.38	$170.40	$170.40
Purchase #2	$97.94	12.552%	$110.2334	$110.23	$110.25	$110.20
Purchase #3	$232.91	11.256%	$259.1263	$259.13	$259.15	$259.10
Purchase #4	$94.45	10.274%	$104.1538	$104.15	$104.15	$104.20
Purchase #5	$79.68	13.856%	$90.7205	$90.72	$90.70	$90.70
Purchase #6	$95.42	11.102%	$106.0135	$106.01	$106.00	$106.00
Purchase #7	$56.82	5.322%	$59.844	$59.84	$59.85	$59.80
7 purchase totals =	$819.16		$900.4734	$900.46	$900.50	$900.40