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	$57.62	3.758%	$59.7854	$59.79	$59.80	$59.80
Purchase #2	$50.57	8.431%	$54.8336	$54.83	$54.85	$54.80
Purchase #3	$52.77	8.531%	$57.2718	$57.27	$57.25	$57.30
Purchase #4	$52.89	11.129%	$58.7761	$58.78	$58.80	$58.80
Purchase #5	$194.36	11.250%	$216.2255	$216.23	$216.25	$216.20
Purchase #6	$242.84	5.420%	$256.0019	$256.00	$256.00	$256.00
Purchase #7	$95.26	9.722%	$104.5212	$104.52	$104.50	$104.50
7 purchase totals =	$746.31		$807.4155	$807.42	$807.45	$807.40