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	$49.60	12.514%	$55.8069	$55.81	$55.80	$55.80
Purchase #2	$55.75	8.395%	$60.4302	$60.43	$60.45	$60.40
Purchase #3	$176.81	3.752%	$183.4439	$183.44	$183.45	$183.40
Purchase #4	$174.46	3.119%	$179.9014	$179.90	$179.90	$179.90
Purchase #5	$83.44	5.783%	$88.2653	$88.27	$88.25	$88.30
Purchase #6	$166.83	11.749%	$186.4309	$186.43	$186.45	$186.40
Purchase #7	$241.39	3.182%	$249.071	$249.07	$249.05	$249.10
7 purchase totals =	$948.28		$1,003.3496	$1,003.35	$1,003.35	$1,003.30