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	$249.27	12.228%	$279.7507	$279.75	$279.75	$279.80
Purchase #2	$150.90	7.691%	$162.5057	$162.51	$162.50	$162.50
Purchase #3	$111.81	10.475%	$123.5221	$123.52	$123.50	$123.50
Purchase #4	$143.53	11.659%	$160.2642	$160.26	$160.25	$160.30
Purchase #5	$153.52	8.446%	$166.4863	$166.49	$166.50	$166.50
Purchase #6	$138.75	5.171%	$145.9248	$145.92	$145.90	$145.90
Purchase #7	$120.98	7.636%	$130.218	$130.22	$130.20	$130.20
7 purchase totals =	$1,068.76		$1,168.6718	$1,168.67	$1,168.60	$1,168.70