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	$141.96	6.169%	$150.7175	$150.72	$150.70	$150.70
Purchase #2	$225.46	3.586%	$233.545	$233.55	$233.55	$233.50
Purchase #3	$47.78	10.263%	$52.6837	$52.68	$52.70	$52.70
Purchase #4	$28.64	13.513%	$32.5101	$32.51	$32.50	$32.50
Purchase #5	$222.85	8.370%	$241.5025	$241.50	$241.50	$241.50
Purchase #6	$41.68	8.205%	$45.0998	$45.10	$45.10	$45.10
Purchase #7	$142.31	9.680%	$156.0856	$156.09	$156.10	$156.10
7 purchase totals =	$850.68		$912.1442	$912.15	$912.15	$912.10