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	$80.42	12.653%	$90.5955	$90.60	$90.60	$90.60
Purchase #2	$28.89	11.323%	$32.1612	$32.16	$32.15	$32.20
Purchase #3	$27.72	13.319%	$31.412	$31.41	$31.40	$31.40
Purchase #4	$217.94	7.206%	$233.6448	$233.64	$233.65	$233.60
Purchase #5	$19.70	10.625%	$21.7931	$21.79	$21.80	$21.80
Purchase #6	$122.82	13.526%	$139.4326	$139.43	$139.45	$139.40
Purchase #7	$121.64	5.845%	$128.7499	$128.75	$128.75	$128.70
7 purchase totals =	$619.13		$677.7891	$677.78	$677.80	$677.70