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	$60.82	4.439%	$63.5198	$63.52	$63.50	$63.50
Purchase #2	$166.48	5.583%	$175.7746	$175.77	$175.75	$175.80
Purchase #3	$27.51	3.736%	$28.5378	$28.54	$28.55	$28.50
Purchase #4	$148.89	3.571%	$154.2069	$154.21	$154.20	$154.20
Purchase #5	$53.97	10.335%	$59.5478	$59.55	$59.55	$59.50
Purchase #6	$29.51	9.338%	$32.2656	$32.27	$32.25	$32.30
Purchase #7	$73.28	6.461%	$78.0146	$78.01	$78.00	$78.00
7 purchase totals =	$560.46		$591.8671	$591.87	$591.80	$591.80