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	$31.95	10.782%	$35.3948	$35.39	$35.40	$35.40
Purchase #2	$146.42	3.812%	$152.0015	$152.00	$152.00	$152.00
Purchase #3	$108.90	4.773%	$114.0978	$114.10	$114.10	$114.10
Purchase #4	$216.69	10.193%	$238.7772	$238.78	$238.80	$238.80
Purchase #5	$95.82	13.575%	$108.8276	$108.83	$108.85	$108.80
Purchase #6	$135.75	8.521%	$147.3173	$147.32	$147.30	$147.30
Purchase #7	$104.59	11.346%	$116.4568	$116.46	$116.45	$116.50
7 purchase totals =	$840.12		$912.8730	$912.88	$912.90	$912.90