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	$39.89	3.267%	$41.1932	$41.19	$41.20	$41.20
Purchase #2	$61.95	6.438%	$65.9383	$65.94	$65.95	$65.90
Purchase #3	$101.64	5.188%	$106.9131	$106.91	$106.90	$106.90
Purchase #4	$24.77	10.310%	$27.3238	$27.32	$27.30	$27.30
Purchase #5	$182.35	12.105%	$204.4235	$204.42	$204.40	$204.40
Purchase #6	$148.71	10.333%	$164.0762	$164.08	$164.10	$164.10
Purchase #7	$101.86	9.748%	$111.7893	$111.79	$111.80	$111.80
7 purchase totals =	$661.17		$721.6574	$721.65	$721.65	$721.60