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	$223.40	12.569%	$251.4791	$251.48	$251.50	$251.50
Purchase #2	$143.36	3.341%	$148.1497	$148.15	$148.15	$148.10
Purchase #3	$109.50	7.665%	$117.8932	$117.89	$117.90	$117.90
Purchase #4	$71.77	12.723%	$80.9013	$80.90	$80.90	$80.90
Purchase #5	$184.92	12.760%	$208.5158	$208.52	$208.50	$208.50
Purchase #6	$184.26	4.406%	$192.3785	$192.38	$192.40	$192.40
Purchase #7	$94.70	9.627%	$103.8168	$103.82	$103.80	$103.80
7 purchase totals =	$1,011.91		$1,103.1344	$1,103.14	$1,103.15	$1,103.10