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	$28.54	6.745%	$30.465	$30.47	$30.45	$30.50
Purchase #2	$44.80	8.280%	$48.5094	$48.51	$48.50	$48.50
Purchase #3	$41.29	6.270%	$43.8789	$43.88	$43.90	$43.90
Purchase #4	$100.90	10.660%	$111.6559	$111.66	$111.65	$111.70
Purchase #5	$210.89	5.105%	$221.6559	$221.66	$221.65	$221.70
Purchase #6	$30.26	11.274%	$33.6715	$33.67	$33.65	$33.70
Purchase #7	$161.61	10.171%	$178.0474	$178.05	$178.05	$178.00
7 purchase totals =	$618.29		$667.8840	$667.90	$667.85	$668.00