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	$72.98	11.635%	$81.4712	$81.47	$81.45	$81.50
Purchase #2	$176.95	4.147%	$184.2881	$184.29	$184.30	$184.30
Purchase #3	$38.42	13.778%	$43.7135	$43.71	$43.70	$43.70
Purchase #4	$103.51	10.528%	$114.4075	$114.41	$114.40	$114.40
Purchase #5	$115.62	10.164%	$127.3716	$127.37	$127.35	$127.40
Purchase #6	$103.87	12.665%	$117.0251	$117.03	$117.05	$117.00
Purchase #7	$219.81	5.821%	$232.6051	$232.61	$232.60	$232.60
7 purchase totals =	$831.16		$900.8821	$900.89	$900.85	$900.90