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	$46.86	8.368%	$50.7812	$50.78	$50.80	$50.80
Purchase #2	$84.65	6.872%	$90.4671	$90.47	$90.45	$90.50
Purchase #3	$26.67	5.284%	$28.0792	$28.08	$28.10	$28.10
Purchase #4	$228.91	6.833%	$244.5514	$244.55	$244.55	$244.60
Purchase #5	$49.38	10.287%	$54.4597	$54.46	$54.45	$54.50
Purchase #6	$61.28	8.863%	$66.7112	$66.71	$66.70	$66.70
Purchase #7	$94.40	11.805%	$105.5439	$105.54	$105.55	$105.50
7 purchase totals =	$592.15		$640.5937	$640.59	$640.60	$640.70