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	$172.99	10.367%	$190.9239	$190.92	$190.90	$190.90
Purchase #2	$49.34	9.284%	$53.9207	$53.92	$53.90	$53.90
Purchase #3	$203.61	13.861%	$231.8324	$231.83	$231.85	$231.80
Purchase #4	$169.27	12.341%	$190.1596	$190.16	$190.15	$190.20
Purchase #5	$115.71	6.331%	$123.0356	$123.04	$123.05	$123.00
Purchase #6	$83.40	4.639%	$87.2689	$87.27	$87.25	$87.30
Purchase #7	$11.48	8.152%	$12.4158	$12.42	$12.40	$12.40
7 purchase totals =	$805.80		$889.5569	$889.56	$889.50	$889.50