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	$203.47	9.821%	$223.4528	$223.45	$223.45	$223.50
Purchase #2	$76.39	6.245%	$81.1606	$81.16	$81.15	$81.20
Purchase #3	$69.29	9.465%	$75.8483	$75.85	$75.85	$75.80
Purchase #4	$151.92	4.225%	$158.3386	$158.34	$158.35	$158.30
Purchase #5	$20.29	9.856%	$22.2898	$22.29	$22.30	$22.30
Purchase #6	$29.28	13.779%	$33.3145	$33.31	$33.30	$33.30
Purchase #7	$81.84	10.434%	$90.3792	$90.38	$90.40	$90.40
7 purchase totals =	$632.48		$684.7838	$684.78	$684.80	$684.80