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	$65.88	13.114%	$74.5195	$74.52	$74.50	$74.50
Purchase #2	$168.39	4.770%	$176.4222	$176.42	$176.40	$176.40
Purchase #3	$241.40	5.353%	$254.3221	$254.32	$254.30	$254.30
Purchase #4	$116.61	10.491%	$128.8436	$128.84	$128.85	$128.80
Purchase #5	$65.83	9.158%	$71.8587	$71.86	$71.85	$71.90
Purchase #6	$157.81	4.380%	$164.7221	$164.72	$164.70	$164.70
Purchase #7	$45.27	13.306%	$51.2936	$51.29	$51.30	$51.30
7 purchase totals =	$861.19		$921.9818	$921.97	$921.90	$921.90