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	$107.33	10.323%	$118.4097	$118.41	$118.40	$118.40
Purchase #2	$124.38	12.193%	$139.5457	$139.55	$139.55	$139.50
Purchase #3	$102.44	8.690%	$111.342	$111.34	$111.35	$111.30
Purchase #4	$34.67	13.308%	$39.2839	$39.28	$39.30	$39.30
Purchase #5	$143.98	5.771%	$152.2891	$152.29	$152.30	$152.30
Purchase #6	$193.71	7.158%	$207.5758	$207.58	$207.60	$207.60
Purchase #7	$196.34	12.603%	$221.0847	$221.08	$221.10	$221.10
7 purchase totals =	$902.85		$989.5309	$989.53	$989.60	$989.50