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	$115.41	7.116%	$123.6226	$123.62	$123.60	$123.60
Purchase #2	$183.28	5.185%	$192.7831	$192.78	$192.80	$192.80
Purchase #3	$140.92	9.131%	$153.7874	$153.79	$153.80	$153.80
Purchase #4	$112.93	3.289%	$116.6443	$116.64	$116.65	$116.60
Purchase #5	$116.58	12.362%	$130.9916	$130.99	$131.00	$131.00
Purchase #6	$78.33	6.439%	$83.3737	$83.37	$83.35	$83.40
Purchase #7	$39.91	7.468%	$42.8905	$42.89	$42.90	$42.90
7 purchase totals =	$787.36		$844.0932	$844.08	$844.10	$844.10