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	$192.83	10.660%	$213.3857	$213.39	$213.40	$213.40
Purchase #2	$88.26	12.647%	$99.4222	$99.42	$99.40	$99.40
Purchase #3	$146.50	9.645%	$160.6299	$160.63	$160.65	$160.60
Purchase #4	$81.54	10.672%	$90.2419	$90.24	$90.25	$90.20
Purchase #5	$48.51	7.748%	$52.2686	$52.27	$52.25	$52.30
Purchase #6	$14.66	5.533%	$15.4711	$15.47	$15.45	$15.50
Purchase #7	$179.60	8.793%	$195.3922	$195.39	$195.40	$195.40
7 purchase totals =	$751.90		$826.8116	$826.81	$826.80	$826.80