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	$111.47	10.584%	$123.268	$123.27	$123.25	$123.30
Purchase #2	$91.88	6.129%	$97.5113	$97.51	$97.50	$97.50
Purchase #3	$91.89	9.266%	$100.4045	$100.40	$100.40	$100.40
Purchase #4	$113.50	8.649%	$123.3166	$123.32	$123.30	$123.30
Purchase #5	$135.98	11.500%	$151.6177	$151.62	$151.60	$151.60
Purchase #6	$249.71	5.471%	$263.3716	$263.37	$263.35	$263.40
Purchase #7	$107.80	7.347%	$115.7201	$115.72	$115.70	$115.70
7 purchase totals =	$902.23		$975.2098	$975.21	$975.10	$975.20