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	$139.77	3.321%	$144.4118	$144.41	$144.40	$144.40
Purchase #2	$101.73	10.295%	$112.2031	$112.20	$112.20	$112.20
Purchase #3	$20.75	5.759%	$21.945	$21.95	$21.95	$21.90
Purchase #4	$188.53	13.747%	$214.4472	$214.45	$214.45	$214.40
Purchase #5	$58.96	12.406%	$66.2746	$66.27	$66.25	$66.30
Purchase #6	$30.67	9.574%	$33.6063	$33.61	$33.60	$33.60
Purchase #7	$64.46	4.835%	$67.5766	$67.58	$67.60	$67.60
7 purchase totals =	$604.87		$660.4646	$660.47	$660.45	$660.40