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	$12.36	9.152%	$13.4912	$13.49	$13.50	$13.50
Purchase #2	$57.53	5.363%	$60.6153	$60.62	$60.60	$60.60
Purchase #3	$200.42	12.672%	$225.8172	$225.82	$225.80	$225.80
Purchase #4	$36.64	4.113%	$38.147	$38.15	$38.15	$38.10
Purchase #5	$220.56	6.210%	$234.2568	$234.26	$234.25	$234.30
Purchase #6	$92.25	8.606%	$100.189	$100.19	$100.20	$100.20
Purchase #7	$209.53	11.386%	$233.3871	$233.39	$233.40	$233.40
7 purchase totals =	$829.29		$905.9036	$905.92	$905.90	$905.90