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	$61.74	8.314%	$66.8731	$66.87	$66.85	$66.90
Purchase #2	$157.67	7.779%	$169.9351	$169.94	$169.95	$169.90
Purchase #3	$171.75	11.824%	$192.0577	$192.06	$192.05	$192.10
Purchase #4	$144.67	10.225%	$159.4625	$159.46	$159.45	$159.50
Purchase #5	$225.49	4.434%	$235.4882	$235.49	$235.50	$235.50
Purchase #6	$99.30	12.234%	$111.4484	$111.45	$111.45	$111.40
Purchase #7	$46.88	10.752%	$51.9205	$51.92	$51.90	$51.90
7 purchase totals =	$907.50		$987.1855	$987.19	$987.15	$987.20