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	$217.32	3.286%	$224.4611	$224.46	$224.45	$224.50
Purchase #2	$250.76	8.755%	$272.714	$272.71	$272.70	$272.70
Purchase #3	$50.34	13.188%	$56.9788	$56.98	$57.00	$57.00
Purchase #4	$148.50	7.764%	$160.0295	$160.03	$160.05	$160.00
Purchase #5	$80.49	11.218%	$89.5194	$89.52	$89.50	$89.50
Purchase #6	$38.36	8.590%	$41.6551	$41.66	$41.65	$41.70
Purchase #7	$99.34	12.591%	$111.8479	$111.85	$111.85	$111.80
7 purchase totals =	$885.11		$957.2058	$957.21	$957.20	$957.20