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	$177.52	6.790%	$189.5736	$189.57	$189.55	$189.60
Purchase #2	$81.66	5.669%	$86.2893	$86.29	$86.30	$86.30
Purchase #3	$65.28	10.415%	$72.0789	$72.08	$72.10	$72.10
Purchase #4	$90.63	11.336%	$100.9038	$100.90	$100.90	$100.90
Purchase #5	$87.30	13.186%	$98.8114	$98.81	$98.80	$98.80
Purchase #6	$10.64	3.161%	$10.9763	$10.98	$11.00	$11.00
Purchase #7	$119.32	10.453%	$131.7925	$131.79	$131.80	$131.80
7 purchase totals =	$632.35		$690.4258	$690.42	$690.45	$690.50