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	$109.53	4.835%	$114.8258	$114.83	$114.85	$114.80
Purchase #2	$138.39	5.559%	$146.0831	$146.08	$146.10	$146.10
Purchase #3	$94.80	11.726%	$105.9162	$105.92	$105.90	$105.90
Purchase #4	$99.56	11.578%	$111.0871	$111.09	$111.10	$111.10
Purchase #5	$49.62	9.328%	$54.2486	$54.25	$54.25	$54.20
Purchase #6	$14.80	7.740%	$15.9455	$15.95	$15.95	$15.90
Purchase #7	$77.60	3.215%	$80.0948	$80.09	$80.10	$80.10
7 purchase totals =	$584.30		$628.2011	$628.21	$628.25	$628.10