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	$16.44	12.554%	$18.5039	$18.50	$18.50	$18.50
Purchase #2	$43.49	4.123%	$45.2831	$45.28	$45.30	$45.30
Purchase #3	$192.27	9.523%	$210.5799	$210.58	$210.60	$210.60
Purchase #4	$155.89	7.599%	$167.7361	$167.74	$167.75	$167.70
Purchase #5	$15.98	12.231%	$17.9345	$17.93	$17.95	$17.90
Purchase #6	$11.35	6.649%	$12.1047	$12.10	$12.10	$12.10
Purchase #7	$38.74	13.253%	$43.8742	$43.87	$43.85	$43.90
7 purchase totals =	$474.16		$516.0164	$516.00	$516.05	$516.00