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	$148.97	10.790%	$165.0439	$165.04	$165.05	$165.00
Purchase #2	$42.72	9.546%	$46.7981	$46.80	$46.80	$46.80
Purchase #3	$121.69	8.845%	$132.4535	$132.45	$132.45	$132.50
Purchase #4	$100.74	13.842%	$114.6844	$114.68	$114.70	$114.70
Purchase #5	$6.52	5.618%	$6.8863	$6.89	$6.90	$6.90
Purchase #6	$89.86	12.373%	$100.9784	$100.98	$101.00	$101.00
Purchase #7	$243.92	11.466%	$271.8879	$271.89	$271.90	$271.90
7 purchase totals =	$754.42		$838.7325	$838.73	$838.80	$838.80