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	$180.46	5.717%	$190.7769	$190.78	$190.80	$190.80
Purchase #2	$111.49	4.333%	$116.3209	$116.32	$116.30	$116.30
Purchase #3	$17.25	3.504%	$17.8544	$17.85	$17.85	$17.90
Purchase #4	$33.71	12.264%	$37.8442	$37.84	$37.85	$37.80
Purchase #5	$11.67	12.328%	$13.1087	$13.11	$13.10	$13.10
Purchase #6	$194.43	7.291%	$208.6059	$208.61	$208.60	$208.60
Purchase #7	$112.45	13.317%	$127.425	$127.43	$127.45	$127.40
7 purchase totals =	$661.46		$711.9360	$711.94	$711.95	$711.90