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	$79.38	13.762%	$90.3043	$90.30	$90.30	$90.30
Purchase #2	$50.50	10.470%	$55.7874	$55.79	$55.80	$55.80
Purchase #3	$105.25	7.244%	$112.8743	$112.87	$112.85	$112.90
Purchase #4	$238.39	11.218%	$265.1326	$265.13	$265.15	$265.10
Purchase #5	$11.85	10.402%	$13.0826	$13.08	$13.10	$13.10
Purchase #6	$205.65	11.114%	$228.5059	$228.51	$228.50	$228.50
Purchase #7	$119.63	3.163%	$123.4139	$123.41	$123.40	$123.40
7 purchase totals =	$810.65		$889.1010	$889.09	$889.10	$889.10