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	$10.50	12.487%	$11.8111	$11.81	$11.80	$11.80
Purchase #2	$40.74	9.485%	$44.6042	$44.60	$44.60	$44.60
Purchase #3	$43.58	13.121%	$49.2981	$49.30	$49.30	$49.30
Purchase #4	$42.89	13.819%	$48.817	$48.82	$48.80	$48.80
Purchase #5	$169.52	13.209%	$191.9119	$191.91	$191.90	$191.90
Purchase #6	$178.70	4.702%	$187.1025	$187.10	$187.10	$187.10
Purchase #7	$79.65	12.822%	$89.8627	$89.86	$89.85	$89.90
7 purchase totals =	$565.58		$623.4075	$623.40	$623.35	$623.40