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	$46.99	7.296%	$50.4184	$50.42	$50.40	$50.40
Purchase #2	$225.49	4.703%	$236.0948	$236.09	$236.10	$236.10
Purchase #3	$222.74	8.322%	$241.2764	$241.28	$241.30	$241.30
Purchase #4	$98.27	5.153%	$103.3339	$103.33	$103.35	$103.30
Purchase #5	$42.95	13.140%	$48.5936	$48.59	$48.60	$48.60
Purchase #6	$89.39	10.726%	$98.978	$98.98	$99.00	$99.00
Purchase #7	$12.88	12.191%	$14.4502	$14.45	$14.45	$14.50
7 purchase totals =	$738.71		$793.1453	$793.14	$793.20	$793.20