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	$108.63	9.253%	$118.6815	$118.68	$118.70	$118.70
Purchase #2	$181.90	8.314%	$197.0232	$197.02	$197.00	$197.00
Purchase #3	$50.27	5.541%	$53.0555	$53.06	$53.05	$53.10
Purchase #4	$166.66	3.243%	$172.0648	$172.06	$172.05	$172.10
Purchase #5	$137.78	11.308%	$153.3602	$153.36	$153.35	$153.40
Purchase #6	$40.72	6.369%	$43.3135	$43.31	$43.30	$43.30
Purchase #7	$158.59	8.681%	$172.3572	$172.36	$172.35	$172.40
7 purchase totals =	$844.55		$909.8559	$909.85	$909.80	$910.00