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	$170.77	6.493%	$181.8581	$181.86	$181.85	$181.90
Purchase #2	$97.95	11.709%	$109.419	$109.42	$109.40	$109.40
Purchase #3	$92.39	7.852%	$99.6445	$99.64	$99.65	$99.60
Purchase #4	$54.40	6.792%	$58.0948	$58.09	$58.10	$58.10
Purchase #5	$27.63	4.746%	$28.9413	$28.94	$28.95	$28.90
Purchase #6	$60.46	5.278%	$63.6511	$63.65	$63.65	$63.70
Purchase #7	$34.82	10.541%	$38.4904	$38.49	$38.50	$38.50
7 purchase totals =	$538.42		$580.0992	$580.09	$580.10	$580.10