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	$127.32	9.182%	$139.0105	$139.01	$139.00	$139.00
Purchase #2	$45.82	9.343%	$50.101	$50.10	$50.10	$50.10
Purchase #3	$103.95	7.530%	$111.7774	$111.78	$111.80	$111.80
Purchase #4	$228.62	4.197%	$238.2152	$238.22	$238.20	$238.20
Purchase #5	$70.95	8.734%	$77.1468	$77.15	$77.15	$77.10
Purchase #6	$196.47	9.483%	$215.1013	$215.10	$215.10	$215.10
Purchase #7	$164.66	6.437%	$175.2592	$175.26	$175.25	$175.30
7 purchase totals =	$937.79		$1,006.6114	$1,006.62	$1,006.60	$1,006.60