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	$13.78	9.535%	$15.0939	$15.09	$15.10	$15.10
Purchase #2	$10.61	6.525%	$11.3023	$11.30	$11.30	$11.30
Purchase #3	$194.82	8.105%	$210.6102	$210.61	$210.60	$210.60
Purchase #4	$19.36	10.514%	$21.3955	$21.40	$21.40	$21.40
Purchase #5	$21.50	10.490%	$23.7554	$23.76	$23.75	$23.80
Purchase #6	$88.81	12.330%	$99.7603	$99.76	$99.75	$99.80
Purchase #7	$118.39	10.635%	$130.9808	$130.98	$131.00	$131.00
7 purchase totals =	$467.27		$512.8984	$512.90	$512.90	$513.00