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	$16.61	13.312%	$18.8211	$18.82	$18.80	$18.80
Purchase #2	$184.88	11.308%	$205.7862	$205.79	$205.80	$205.80
Purchase #3	$97.78	5.450%	$103.109	$103.11	$103.10	$103.10
Purchase #4	$16.87	11.413%	$18.7954	$18.80	$18.80	$18.80
Purchase #5	$84.40	7.738%	$90.9309	$90.93	$90.95	$90.90
Purchase #6	$246.29	10.233%	$271.4929	$271.49	$271.50	$271.50
Purchase #7	$19.77	11.227%	$21.9896	$21.99	$22.00	$22.00
7 purchase totals =	$666.60		$730.9251	$730.93	$730.95	$730.90