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	$141.38	12.164%	$158.5775	$158.58	$158.60	$158.60
Purchase #2	$157.28	9.440%	$172.1272	$172.13	$172.15	$172.10
Purchase #3	$38.32	9.842%	$42.0915	$42.09	$42.10	$42.10
Purchase #4	$147.32	4.222%	$153.5399	$153.54	$153.55	$153.50
Purchase #5	$26.71	4.128%	$27.8126	$27.81	$27.80	$27.80
Purchase #6	$73.31	9.465%	$80.2488	$80.25	$80.25	$80.20
Purchase #7	$14.60	8.726%	$15.874	$15.87	$15.85	$15.90
7 purchase totals =	$598.92		$650.2715	$650.27	$650.30	$650.20