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	$241.28	4.649%	$252.4971	$252.50	$252.50	$252.50
Purchase #2	$81.44	8.152%	$88.079	$88.08	$88.10	$88.10
Purchase #3	$18.70	12.834%	$21.1	$21.10	$21.10	$21.10
Purchase #4	$237.61	3.164%	$245.128	$245.13	$245.15	$245.10
Purchase #5	$173.33	13.328%	$196.4314	$196.43	$196.45	$196.40
Purchase #6	$235.83	12.556%	$265.4408	$265.44	$265.45	$265.40
Purchase #7	$29.57	10.487%	$32.671	$32.67	$32.65	$32.70
7 purchase totals =	$1,017.76		$1,101.3473	$1,101.35	$1,101.40	$1,101.30