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	$93.67	6.196%	$99.4738	$99.47	$99.45	$99.50
Purchase #2	$53.38	5.322%	$56.2209	$56.22	$56.20	$56.20
Purchase #3	$237.80	8.572%	$258.1842	$258.18	$258.20	$258.20
Purchase #4	$36.45	10.818%	$40.3932	$40.39	$40.40	$40.40
Purchase #5	$238.37	4.634%	$249.4161	$249.42	$249.40	$249.40
Purchase #6	$27.85	5.129%	$29.2784	$29.28	$29.30	$29.30
Purchase #7	$194.71	10.229%	$214.6269	$214.63	$214.65	$214.60
7 purchase totals =	$882.23		$947.5935	$947.59	$947.60	$947.60