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	$247.78	12.868%	$279.6643	$279.66	$279.65	$279.70
Purchase #2	$35.55	9.370%	$38.881	$38.88	$38.90	$38.90
Purchase #3	$39.26	8.547%	$42.6156	$42.62	$42.60	$42.60
Purchase #4	$12.57	13.453%	$14.261	$14.26	$14.25	$14.30
Purchase #5	$146.31	6.710%	$156.1274	$156.13	$156.15	$156.10
Purchase #6	$114.31	4.273%	$119.1945	$119.19	$119.20	$119.20
Purchase #7	$93.80	10.683%	$103.8207	$103.82	$103.80	$103.80
7 purchase totals =	$689.58		$754.5645	$754.56	$754.55	$754.60