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	$10.50	12.234%	$11.7846	$11.78	$11.80	$11.80
Purchase #2	$129.66	9.340%	$141.7702	$141.77	$141.75	$141.80
Purchase #3	$69.97	11.787%	$78.2174	$78.22	$78.20	$78.20
Purchase #4	$214.60	11.710%	$239.7297	$239.73	$239.75	$239.70
Purchase #5	$20.54	6.729%	$21.9221	$21.92	$21.90	$21.90
Purchase #6	$132.56	9.850%	$145.6172	$145.62	$145.60	$145.60
Purchase #7	$134.95	4.629%	$141.1968	$141.20	$141.20	$141.20
7 purchase totals =	$712.78		$780.2380	$780.24	$780.20	$780.20