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	$70.78	6.104%	$75.1004	$75.10	$75.10	$75.10
Purchase #2	$44.39	11.395%	$49.4482	$49.45	$49.45	$49.40
Purchase #3	$64.90	10.858%	$71.9468	$71.95	$71.95	$71.90
Purchase #4	$9.87	7.488%	$10.6091	$10.61	$10.60	$10.60
Purchase #5	$160.25	8.342%	$173.6181	$173.62	$173.60	$173.60
Purchase #6	$159.78	12.425%	$179.6327	$179.63	$179.65	$179.60
Purchase #7	$81.82	10.542%	$90.4455	$90.45	$90.45	$90.40
7 purchase totals =	$591.79		$650.8008	$650.81	$650.80	$650.60