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	$170.57	11.642%	$190.4278	$190.43	$190.45	$190.40
Purchase #2	$164.57	13.493%	$186.7754	$186.78	$186.80	$186.80
Purchase #3	$19.46	7.527%	$20.9248	$20.92	$20.90	$20.90
Purchase #4	$131.46	13.509%	$149.2189	$149.22	$149.20	$149.20
Purchase #5	$40.97	3.499%	$42.4035	$42.40	$42.40	$42.40
Purchase #6	$57.30	3.223%	$59.1468	$59.15	$59.15	$59.10
Purchase #7	$16.62	7.601%	$17.8833	$17.88	$17.90	$17.90
7 purchase totals =	$600.95		$666.7805	$666.78	$666.80	$666.70