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	$147.83	7.554%	$158.9971	$159.00	$159.00	$159.00
Purchase #2	$106.55	4.743%	$111.6037	$111.60	$111.60	$111.60
Purchase #3	$245.76	9.467%	$269.0261	$269.03	$269.05	$269.00
Purchase #4	$223.52	11.688%	$249.645	$249.65	$249.65	$249.60
Purchase #5	$49.40	5.857%	$52.2934	$52.29	$52.30	$52.30
Purchase #6	$48.43	8.732%	$52.6589	$52.66	$52.65	$52.70
Purchase #7	$38.77	11.678%	$43.2976	$43.30	$43.30	$43.30
7 purchase totals =	$860.26		$937.5218	$937.53	$937.55	$937.50