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	$154.76	6.776%	$165.2465	$165.25	$165.25	$165.20
Purchase #2	$227.79	4.719%	$238.5394	$238.54	$238.55	$238.50
Purchase #3	$112.27	4.111%	$116.8854	$116.89	$116.90	$116.90
Purchase #4	$38.25	3.768%	$39.6913	$39.69	$39.70	$39.70
Purchase #5	$85.64	7.834%	$92.349	$92.35	$92.35	$92.30
Purchase #6	$28.68	11.798%	$32.0637	$32.06	$32.05	$32.10
Purchase #7	$150.32	9.789%	$165.0348	$165.03	$165.05	$165.00
7 purchase totals =	$797.71		$849.8101	$849.81	$849.85	$849.70