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	$231.60	8.128%	$250.4244	$250.42	$250.40	$250.40
Purchase #2	$6.73	7.749%	$7.2515	$7.25	$7.25	$7.30
Purchase #3	$101.91	3.573%	$105.5512	$105.55	$105.55	$105.60
Purchase #4	$111.95	6.410%	$119.126	$119.13	$119.15	$119.10
Purchase #5	$138.25	12.792%	$155.9349	$155.93	$155.95	$155.90
Purchase #6	$63.68	13.739%	$72.429	$72.43	$72.45	$72.40
Purchase #7	$184.71	13.197%	$209.0862	$209.09	$209.10	$209.10
7 purchase totals =	$838.83		$919.8032	$919.80	$919.85	$919.80