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	$17.29	8.713%	$18.7965	$18.80	$18.80	$18.80
Purchase #2	$233.50	13.298%	$264.5508	$264.55	$264.55	$264.60
Purchase #3	$214.99	3.415%	$222.3319	$222.33	$222.35	$222.30
Purchase #4	$237.33	11.401%	$264.388	$264.39	$264.40	$264.40
Purchase #5	$17.33	6.669%	$18.4857	$18.49	$18.50	$18.50
Purchase #6	$16.64	9.423%	$18.208	$18.21	$18.20	$18.20
Purchase #7	$144.60	7.776%	$155.8441	$155.84	$155.85	$155.80
7 purchase totals =	$881.68		$962.6050	$962.61	$962.65	$962.60