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	$114.67	13.343%	$129.9704	$129.97	$129.95	$130.00
Purchase #2	$148.77	11.655%	$166.1091	$166.11	$166.10	$166.10
Purchase #3	$133.66	13.247%	$151.3659	$151.37	$151.35	$151.40
Purchase #4	$164.53	5.370%	$173.3653	$173.37	$173.35	$173.40
Purchase #5	$164.43	3.683%	$170.486	$170.49	$170.50	$170.50
Purchase #6	$134.82	7.798%	$145.3333	$145.33	$145.35	$145.30
Purchase #7	$38.83	6.773%	$41.46	$41.46	$41.45	$41.50
7 purchase totals =	$899.71		$978.0900	$978.10	$978.05	$978.20