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	$99.38	12.404%	$111.7071	$111.71	$111.70	$111.70
Purchase #2	$214.95	12.535%	$241.894	$241.89	$241.90	$241.90
Purchase #3	$237.49	13.724%	$270.0831	$270.08	$270.10	$270.10
Purchase #4	$205.63	13.709%	$233.8198	$233.82	$233.80	$233.80
Purchase #5	$176.98	5.322%	$186.3989	$186.40	$186.40	$186.40
Purchase #6	$95.79	8.822%	$104.2406	$104.24	$104.25	$104.20
Purchase #7	$131.64	12.751%	$148.4254	$148.43	$148.45	$148.40
7 purchase totals =	$1,161.86		$1,296.5689	$1,296.57	$1,296.60	$1,296.50