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	$116.79	10.106%	$128.5928	$128.59	$128.60	$128.60
Purchase #2	$134.42	8.543%	$145.9035	$145.90	$145.90	$145.90
Purchase #3	$54.44	9.835%	$59.7942	$59.79	$59.80	$59.80
Purchase #4	$28.83	5.541%	$30.4275	$30.43	$30.45	$30.40
Purchase #5	$37.57	9.729%	$41.2252	$41.23	$41.25	$41.20
Purchase #6	$207.88	4.433%	$217.0953	$217.10	$217.10	$217.10
Purchase #7	$17.88	3.341%	$18.4774	$18.48	$18.50	$18.50
7 purchase totals =	$597.81		$641.5159	$641.52	$641.60	$641.50