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	$111.40	8.450%	$120.8133	$120.81	$120.80	$120.80
Purchase #2	$49.45	13.144%	$55.9497	$55.95	$55.95	$55.90
Purchase #3	$239.30	8.189%	$258.8963	$258.90	$258.90	$258.90
Purchase #4	$222.91	5.192%	$234.4835	$234.48	$234.50	$234.50
Purchase #5	$31.58	11.631%	$35.2531	$35.25	$35.25	$35.30
Purchase #6	$200.41	13.808%	$228.0826	$228.08	$228.10	$228.10
Purchase #7	$208.51	4.108%	$217.0756	$217.08	$217.10	$217.10
7 purchase totals =	$1,063.56		$1,150.5541	$1,150.55	$1,150.60	$1,150.60