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	$111.68	8.255%	$120.8992	$120.90	$120.90	$120.90
Purchase #2	$65.72	9.352%	$71.8661	$71.87	$71.85	$71.90
Purchase #3	$250.78	8.588%	$272.317	$272.32	$272.30	$272.30
Purchase #4	$167.52	13.363%	$189.9057	$189.91	$189.90	$189.90
Purchase #5	$44.39	4.518%	$46.3955	$46.40	$46.40	$46.40
Purchase #6	$154.76	7.531%	$166.415	$166.42	$166.40	$166.40
Purchase #7	$50.49	4.202%	$52.6116	$52.61	$52.60	$52.60
7 purchase totals =	$845.34		$920.4101	$920.43	$920.35	$920.40