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	$107.43	3.768%	$111.478	$111.48	$111.50	$111.50
Purchase #2	$92.60	12.123%	$103.8259	$103.83	$103.85	$103.80
Purchase #3	$6.87	7.207%	$7.3651	$7.37	$7.35	$7.40
Purchase #4	$39.91	8.229%	$43.1942	$43.19	$43.20	$43.20
Purchase #5	$120.42	4.522%	$125.8654	$125.87	$125.85	$125.90
Purchase #6	$88.25	13.723%	$100.3605	$100.36	$100.35	$100.40
Purchase #7	$89.72	6.792%	$95.8138	$95.81	$95.80	$95.80
7 purchase totals =	$545.20		$587.9029	$587.91	$587.90	$588.00