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	$34.99	8.118%	$37.8305	$37.83	$37.85	$37.80
Purchase #2	$104.49	9.715%	$114.6412	$114.64	$114.65	$114.60
Purchase #3	$92.52	8.655%	$100.5276	$100.53	$100.55	$100.50
Purchase #4	$60.41	10.184%	$66.5622	$66.56	$66.55	$66.60
Purchase #5	$111.74	13.429%	$126.7456	$126.75	$126.75	$126.70
Purchase #6	$218.51	13.867%	$248.8108	$248.81	$248.80	$248.80
Purchase #7	$131.36	6.294%	$139.6278	$139.63	$139.65	$139.60
7 purchase totals =	$754.02		$834.7457	$834.75	$834.80	$834.60