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	$14.91	3.858%	$15.4852	$15.49	$15.50	$15.50
Purchase #2	$85.56	11.260%	$95.1941	$95.19	$95.20	$95.20
Purchase #3	$111.83	10.416%	$123.4782	$123.48	$123.50	$123.50
Purchase #4	$130.87	10.321%	$144.3771	$144.38	$144.40	$144.40
Purchase #5	$11.72	9.746%	$12.8622	$12.86	$12.85	$12.90
Purchase #6	$52.95	6.850%	$56.5771	$56.58	$56.60	$56.60
Purchase #7	$123.51	3.715%	$128.0984	$128.10	$128.10	$128.10
7 purchase totals =	$531.35		$576.0723	$576.08	$576.15	$576.20