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	$246.82	7.578%	$265.524	$265.52	$265.50	$265.50
Purchase #2	$166.29	13.657%	$189.0002	$189.00	$189.00	$189.00
Purchase #3	$6.89	6.299%	$7.324	$7.32	$7.30	$7.30
Purchase #4	$203.29	4.575%	$212.5905	$212.59	$212.60	$212.60
Purchase #5	$69.59	4.745%	$72.892	$72.89	$72.90	$72.90
Purchase #6	$18.87	8.253%	$20.4273	$20.43	$20.45	$20.40
Purchase #7	$56.70	12.451%	$63.7597	$63.76	$63.75	$63.80
7 purchase totals =	$768.45		$831.5177	$831.51	$831.50	$831.50