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	$124.45	11.809%	$139.1463	$139.15	$139.15	$139.10
Purchase #2	$157.77	6.653%	$168.2664	$168.27	$168.25	$168.30
Purchase #3	$74.77	6.764%	$79.8274	$79.83	$79.85	$79.80
Purchase #4	$235.26	13.315%	$266.5849	$266.58	$266.60	$266.60
Purchase #5	$99.35	6.207%	$105.5167	$105.52	$105.50	$105.50
Purchase #6	$147.52	13.402%	$167.2906	$167.29	$167.30	$167.30
Purchase #7	$11.80	4.339%	$12.312	$12.31	$12.30	$12.30
7 purchase totals =	$850.92		$938.9443	$938.95	$938.95	$938.90