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	$111.48	10.591%	$123.2868	$123.29	$123.30	$123.30
Purchase #2	$32.95	4.783%	$34.526	$34.53	$34.55	$34.50
Purchase #3	$48.67	9.277%	$53.1851	$53.19	$53.20	$53.20
Purchase #4	$239.82	7.360%	$257.4708	$257.47	$257.45	$257.50
Purchase #5	$118.55	6.504%	$126.2605	$126.26	$126.25	$126.30
Purchase #6	$92.66	13.620%	$105.2803	$105.28	$105.30	$105.30
Purchase #7	$122.97	13.196%	$139.1971	$139.20	$139.20	$139.20
7 purchase totals =	$767.10		$839.2066	$839.22	$839.25	$839.30