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	$37.39	13.412%	$42.4047	$42.40	$42.40	$42.40
Purchase #2	$188.86	4.857%	$198.0329	$198.03	$198.05	$198.00
Purchase #3	$19.64	5.660%	$20.7516	$20.75	$20.75	$20.80
Purchase #4	$176.74	11.440%	$196.9591	$196.96	$196.95	$197.00
Purchase #5	$19.42	11.752%	$21.7022	$21.70	$21.70	$21.70
Purchase #6	$82.85	8.750%	$90.0994	$90.10	$90.10	$90.10
Purchase #7	$142.36	12.778%	$160.5508	$160.55	$160.55	$160.60
7 purchase totals =	$667.26		$730.5007	$730.49	$730.50	$730.60