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	$146.73	10.288%	$161.8256	$161.83	$161.85	$161.80
Purchase #2	$186.62	5.178%	$196.2832	$196.28	$196.30	$196.30
Purchase #3	$13.37	13.425%	$15.1649	$15.16	$15.15	$15.20
Purchase #4	$165.67	10.683%	$183.3685	$183.37	$183.35	$183.40
Purchase #5	$22.85	11.328%	$25.4384	$25.44	$25.45	$25.40
Purchase #6	$10.83	5.410%	$11.4159	$11.42	$11.40	$11.40
Purchase #7	$40.39	13.732%	$45.9364	$45.94	$45.95	$45.90
7 purchase totals =	$586.46		$639.4329	$639.44	$639.45	$639.40