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	$102.87	13.181%	$116.4293	$116.43	$116.45	$116.40
Purchase #2	$64.40	5.328%	$67.8312	$67.83	$67.85	$67.80
Purchase #3	$141.57	6.224%	$150.3813	$150.38	$150.40	$150.40
Purchase #4	$170.82	6.107%	$181.252	$181.25	$181.25	$181.30
Purchase #5	$42.48	13.431%	$48.1855	$48.19	$48.20	$48.20
Purchase #6	$34.95	10.758%	$38.7099	$38.71	$38.70	$38.70
Purchase #7	$239.73	13.786%	$272.7792	$272.78	$272.80	$272.80
7 purchase totals =	$796.82		$875.5684	$875.57	$875.65	$875.60