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	$125.41	13.684%	$142.5711	$142.57	$142.55	$142.60
Purchase #2	$182.72	3.440%	$189.0056	$189.01	$189.00	$189.00
Purchase #3	$102.87	11.737%	$114.9439	$114.94	$114.95	$114.90
Purchase #4	$40.91	12.856%	$46.1694	$46.17	$46.15	$46.20
Purchase #5	$19.55	10.386%	$21.5805	$21.58	$21.60	$21.60
Purchase #6	$246.87	11.707%	$275.7711	$275.77	$275.75	$275.80
Purchase #7	$191.89	12.379%	$215.6441	$215.64	$215.65	$215.60
7 purchase totals =	$910.22		$1,005.6857	$1,005.68	$1,005.65	$1,005.70