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	$166.96	7.538%	$179.5454	$179.55	$179.55	$179.50
Purchase #2	$100.64	10.704%	$111.4125	$111.41	$111.40	$111.40
Purchase #3	$187.89	5.325%	$197.8951	$197.90	$197.90	$197.90
Purchase #4	$85.91	4.865%	$90.0895	$90.09	$90.10	$90.10
Purchase #5	$16.52	13.338%	$18.7234	$18.72	$18.70	$18.70
Purchase #6	$43.48	8.592%	$47.2158	$47.22	$47.20	$47.20
Purchase #7	$230.26	13.823%	$262.0888	$262.09	$262.10	$262.10
7 purchase totals =	$831.66		$906.9705	$906.98	$906.95	$906.90