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	$38.25	9.573%	$41.9117	$41.91	$41.90	$41.90
Purchase #2	$52.78	13.414%	$59.8599	$59.86	$59.85	$59.90
Purchase #3	$144.44	7.829%	$155.7482	$155.75	$155.75	$155.70
Purchase #4	$166.77	5.772%	$176.396	$176.40	$176.40	$176.40
Purchase #5	$206.29	9.408%	$225.6978	$225.70	$225.70	$225.70
Purchase #6	$249.31	12.139%	$279.5737	$279.57	$279.55	$279.60
Purchase #7	$52.66	13.526%	$59.7828	$59.78	$59.80	$59.80
7 purchase totals =	$910.50		$998.9701	$998.97	$998.95	$999.00