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	$42.25	8.323%	$45.7665	$45.77	$45.75	$45.80
Purchase #2	$171.99	11.404%	$191.6037	$191.60	$191.60	$191.60
Purchase #3	$70.32	3.509%	$72.7875	$72.79	$72.80	$72.80
Purchase #4	$57.77	8.433%	$62.6417	$62.64	$62.65	$62.60
Purchase #5	$217.42	3.853%	$225.7972	$225.80	$225.80	$225.80
Purchase #6	$154.52	12.166%	$173.3189	$173.32	$173.30	$173.30
Purchase #7	$177.25	5.449%	$186.9084	$186.91	$186.90	$186.90
7 purchase totals =	$891.52		$958.8239	$958.83	$958.80	$958.80