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	$237.92	6.476%	$253.3277	$253.33	$253.35	$253.30
Purchase #2	$149.68	5.660%	$158.1519	$158.15	$158.15	$158.20
Purchase #3	$114.51	8.199%	$123.8987	$123.90	$123.90	$123.90
Purchase #4	$112.32	10.180%	$123.7542	$123.75	$123.75	$123.80
Purchase #5	$92.34	13.514%	$104.8188	$104.82	$104.80	$104.80
Purchase #6	$148.79	11.284%	$165.5795	$165.58	$165.60	$165.60
Purchase #7	$192.51	10.715%	$213.1374	$213.14	$213.15	$213.10
7 purchase totals =	$1,048.07		$1,142.6682	$1,142.67	$1,142.70	$1,142.70