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	$9.31	10.636%	$10.3002	$10.30	$10.30	$10.30
Purchase #2	$103.28	3.454%	$106.8473	$106.85	$106.85	$106.80
Purchase #3	$61.57	6.341%	$65.4742	$65.47	$65.45	$65.50
Purchase #4	$237.67	4.859%	$249.2184	$249.22	$249.20	$249.20
Purchase #5	$47.98	7.468%	$51.5631	$51.56	$51.55	$51.60
Purchase #6	$40.85	4.312%	$42.6115	$42.61	$42.60	$42.60
Purchase #7	$26.56	7.602%	$28.5791	$28.58	$28.60	$28.60
7 purchase totals =	$527.22		$554.5938	$554.59	$554.55	$554.60