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	$6.56	4.447%	$6.8517	$6.85	$6.85	$6.90
Purchase #2	$116.97	13.778%	$133.0861	$133.09	$133.10	$133.10
Purchase #3	$168.88	12.650%	$190.2433	$190.24	$190.25	$190.20
Purchase #4	$60.45	11.533%	$67.4217	$67.42	$67.40	$67.40
Purchase #5	$51.30	8.223%	$55.5184	$55.52	$55.50	$55.50
Purchase #6	$247.60	6.378%	$263.3919	$263.39	$263.40	$263.40
Purchase #7	$39.70	8.311%	$42.9995	$43.00	$43.00	$43.00
7 purchase totals =	$691.46		$759.5126	$759.51	$759.50	$759.50