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	$53.95	7.291%	$57.8835	$57.88	$57.90	$57.90
Purchase #2	$95.98	3.651%	$99.4842	$99.48	$99.50	$99.50
Purchase #3	$84.84	6.133%	$90.0432	$90.04	$90.05	$90.00
Purchase #4	$111.64	5.219%	$117.4665	$117.47	$117.45	$117.50
Purchase #5	$12.42	9.434%	$13.5917	$13.59	$13.60	$13.60
Purchase #6	$156.45	6.327%	$166.3486	$166.35	$166.35	$166.30
Purchase #7	$94.65	13.162%	$107.1078	$107.11	$107.10	$107.10
7 purchase totals =	$609.93		$651.9255	$651.92	$651.95	$651.90