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	$227.39	8.602%	$246.9501	$246.95	$246.95	$247.00
Purchase #2	$35.48	12.225%	$39.8174	$39.82	$39.80	$39.80
Purchase #3	$38.33	6.596%	$40.8582	$40.86	$40.85	$40.90
Purchase #4	$241.99	9.674%	$265.4001	$265.40	$265.40	$265.40
Purchase #5	$118.60	3.713%	$123.0036	$123.00	$123.00	$123.00
Purchase #6	$233.72	12.249%	$262.3484	$262.35	$262.35	$262.30
Purchase #7	$37.58	7.486%	$40.3932	$40.39	$40.40	$40.40
7 purchase totals =	$933.09		$1,018.7710	$1,018.77	$1,018.75	$1,018.80