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	$59.99	10.649%	$66.3783	$66.38	$66.40	$66.40
Purchase #2	$136.88	5.630%	$144.5863	$144.59	$144.60	$144.60
Purchase #3	$128.33	4.726%	$134.3949	$134.39	$134.40	$134.40
Purchase #4	$217.41	3.493%	$225.0041	$225.00	$225.00	$225.00
Purchase #5	$214.33	11.346%	$238.6479	$238.65	$238.65	$238.60
Purchase #6	$117.47	10.492%	$129.795	$129.80	$129.80	$129.80
Purchase #7	$122.33	4.210%	$127.4801	$127.48	$127.50	$127.50
7 purchase totals =	$996.74		$1,066.2866	$1,066.29	$1,066.35	$1,066.30