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	$121.51	8.795%	$132.1968	$132.20	$132.20	$132.20
Purchase #2	$190.86	13.776%	$217.1529	$217.15	$217.15	$217.20
Purchase #3	$34.95	13.340%	$39.6123	$39.61	$39.60	$39.60
Purchase #4	$151.80	11.152%	$168.7287	$168.73	$168.75	$168.70
Purchase #5	$98.56	11.223%	$109.6214	$109.62	$109.60	$109.60
Purchase #6	$66.67	8.420%	$72.2836	$72.28	$72.30	$72.30
Purchase #7	$71.27	9.171%	$77.8062	$77.81	$77.80	$77.80
7 purchase totals =	$735.62		$817.4019	$817.40	$817.40	$817.40