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	$188.94	13.781%	$214.9778	$214.98	$215.00	$215.00
Purchase #2	$114.36	5.203%	$120.3102	$120.31	$120.30	$120.30
Purchase #3	$123.56	4.107%	$128.6346	$128.63	$128.65	$128.60
Purchase #4	$69.99	4.103%	$72.8617	$72.86	$72.85	$72.90
Purchase #5	$102.46	8.589%	$111.2603	$111.26	$111.25	$111.30
Purchase #6	$14.96	4.867%	$15.6881	$15.69	$15.70	$15.70
Purchase #7	$129.62	10.720%	$143.5153	$143.52	$143.50	$143.50
7 purchase totals =	$743.89		$807.2480	$807.25	$807.25	$807.30