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	$166.70	8.398%	$180.6995	$180.70	$180.70	$180.70
Purchase #2	$234.87	8.307%	$254.3807	$254.38	$254.40	$254.40
Purchase #3	$72.55	10.291%	$80.0161	$80.02	$80.00	$80.00
Purchase #4	$111.50	10.746%	$123.4818	$123.48	$123.50	$123.50
Purchase #5	$153.65	4.201%	$160.1048	$160.10	$160.10	$160.10
Purchase #6	$233.52	8.379%	$253.0866	$253.09	$253.10	$253.10
Purchase #7	$31.82	3.871%	$33.0518	$33.05	$33.05	$33.10
7 purchase totals =	$1,004.61		$1,084.8213	$1,084.82	$1,084.85	$1,084.90