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	$39.62	5.363%	$41.7448	$41.74	$41.75	$41.70
Purchase #2	$186.30	10.522%	$205.9025	$205.90	$205.90	$205.90
Purchase #3	$206.39	4.661%	$216.0098	$216.01	$216.00	$216.00
Purchase #4	$87.52	3.595%	$90.6663	$90.67	$90.65	$90.70
Purchase #5	$245.99	3.692%	$255.072	$255.07	$255.05	$255.10
Purchase #6	$28.59	13.565%	$32.4682	$32.47	$32.45	$32.50
Purchase #7	$136.83	7.789%	$147.4877	$147.49	$147.50	$147.50
7 purchase totals =	$931.24		$989.3513	$989.35	$989.30	$989.40