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	$101.63	9.615%	$111.4017	$111.40	$111.40	$111.40
Purchase #2	$108.65	5.134%	$114.2281	$114.23	$114.25	$114.20
Purchase #3	$27.60	4.269%	$28.7782	$28.78	$28.80	$28.80
Purchase #4	$125.58	12.420%	$141.177	$141.18	$141.20	$141.20
Purchase #5	$248.70	6.866%	$265.7757	$265.78	$265.80	$265.80
Purchase #6	$59.83	11.702%	$66.8313	$66.83	$66.85	$66.80
Purchase #7	$176.70	3.312%	$182.5523	$182.55	$182.55	$182.60
7 purchase totals =	$848.69		$910.7443	$910.75	$910.85	$910.80