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	$48.28	12.182%	$54.1615	$54.16	$54.15	$54.20
Purchase #2	$98.28	5.651%	$103.8338	$103.83	$103.85	$103.80
Purchase #3	$87.39	13.794%	$99.4446	$99.44	$99.45	$99.40
Purchase #4	$67.36	8.251%	$72.9179	$72.92	$72.90	$72.90
Purchase #5	$181.46	10.382%	$200.2992	$200.30	$200.30	$200.30
Purchase #6	$236.47	9.178%	$258.1732	$258.17	$258.15	$258.20
Purchase #7	$112.74	3.202%	$116.3499	$116.35	$116.35	$116.30
7 purchase totals =	$831.98		$905.1801	$905.17	$905.15	$905.10