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	$34.56	13.161%	$39.1084	$39.11	$39.10	$39.10
Purchase #2	$37.92	8.167%	$41.0169	$41.02	$41.00	$41.00
Purchase #3	$13.67	11.805%	$15.2837	$15.28	$15.30	$15.30
Purchase #4	$164.32	4.772%	$172.1614	$172.16	$172.15	$172.20
Purchase #5	$119.31	10.548%	$131.8948	$131.89	$131.90	$131.90
Purchase #6	$119.66	3.188%	$123.4748	$123.47	$123.45	$123.50
Purchase #7	$118.27	12.552%	$133.1153	$133.12	$133.10	$133.10
7 purchase totals =	$607.71		$656.0553	$656.05	$656.00	$656.10