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	$110.59	4.546%	$115.6174	$115.62	$115.60	$115.60
Purchase #2	$134.55	4.706%	$140.8819	$140.88	$140.90	$140.90
Purchase #3	$68.86	5.225%	$72.4579	$72.46	$72.45	$72.50
Purchase #4	$108.41	13.130%	$122.6442	$122.64	$122.65	$122.60
Purchase #5	$50.62	5.726%	$53.5185	$53.52	$53.50	$53.50
Purchase #6	$31.70	11.815%	$35.4454	$35.45	$35.45	$35.40
Purchase #7	$18.84	13.181%	$21.3233	$21.32	$21.30	$21.30
7 purchase totals =	$523.57		$561.8886	$561.89	$561.85	$561.80