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	$19.38	10.762%	$21.4657	$21.47	$21.45	$21.50
Purchase #2	$248.97	6.382%	$264.8593	$264.86	$264.85	$264.90
Purchase #3	$239.60	5.109%	$251.8412	$251.84	$251.85	$251.80
Purchase #4	$208.53	6.714%	$222.5307	$222.53	$222.55	$222.50
Purchase #5	$104.59	5.861%	$110.72	$110.72	$110.70	$110.70
Purchase #6	$117.47	8.641%	$127.6206	$127.62	$127.60	$127.60
Purchase #7	$15.66	9.864%	$17.2047	$17.20	$17.20	$17.20
7 purchase totals =	$954.20		$1,016.2422	$1,016.24	$1,016.20	$1,016.20