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	$155.37	3.869%	$161.3813	$161.38	$161.40	$161.40
Purchase #2	$11.61	6.105%	$12.3188	$12.32	$12.30	$12.30
Purchase #3	$138.44	12.460%	$155.6896	$155.69	$155.70	$155.70
Purchase #4	$43.69	11.621%	$48.7672	$48.77	$48.75	$48.80
Purchase #5	$40.49	13.343%	$45.8926	$45.89	$45.90	$45.90
Purchase #6	$122.95	4.427%	$128.393	$128.39	$128.40	$128.40
Purchase #7	$115.77	10.172%	$127.5461	$127.55	$127.55	$127.50
7 purchase totals =	$628.32		$679.9886	$679.99	$680.00	$680.00