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	$158.89	13.779%	$180.7835	$180.78	$180.80	$180.80
Purchase #2	$33.64	13.471%	$38.1716	$38.17	$38.15	$38.20
Purchase #3	$129.35	11.860%	$144.6909	$144.69	$144.70	$144.70
Purchase #4	$6.59	12.826%	$7.4352	$7.44	$7.45	$7.40
Purchase #5	$150.94	5.342%	$159.0032	$159.00	$159.00	$159.00
Purchase #6	$58.47	8.761%	$63.5926	$63.59	$63.60	$63.60
Purchase #7	$11.33	4.104%	$11.795	$11.80	$11.80	$11.80
7 purchase totals =	$549.21		$605.4720	$605.47	$605.50	$605.50