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	$95.69	13.704%	$108.8034	$108.80	$108.80	$108.80
Purchase #2	$94.76	5.228%	$99.7141	$99.71	$99.70	$99.70
Purchase #3	$30.31	11.287%	$33.7311	$33.73	$33.75	$33.70
Purchase #4	$146.95	4.459%	$153.5025	$153.50	$153.50	$153.50
Purchase #5	$53.62	3.338%	$55.4098	$55.41	$55.40	$55.40
Purchase #6	$208.25	6.167%	$221.0928	$221.09	$221.10	$221.10
Purchase #7	$214.50	6.113%	$227.6124	$227.61	$227.60	$227.60
7 purchase totals =	$844.08		$899.8661	$899.85	$899.85	$899.80