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	$185.49	12.352%	$208.4017	$208.40	$208.40	$208.40
Purchase #2	$160.58	7.166%	$172.0872	$172.09	$172.10	$172.10
Purchase #3	$244.55	11.304%	$272.1939	$272.19	$272.20	$272.20
Purchase #4	$206.68	8.304%	$223.8427	$223.84	$223.85	$223.80
Purchase #5	$157.62	9.365%	$172.3811	$172.38	$172.40	$172.40
Purchase #6	$200.42	8.180%	$216.8144	$216.81	$216.80	$216.80
Purchase #7	$238.52	7.242%	$255.7936	$255.79	$255.80	$255.80
7 purchase totals =	$1,393.86		$1,521.5146	$1,521.50	$1,521.55	$1,521.50