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	$37.82	6.137%	$40.141	$40.14	$40.15	$40.10
Purchase #2	$132.50	13.509%	$150.3994	$150.40	$150.40	$150.40
Purchase #3	$227.65	9.398%	$249.0445	$249.04	$249.05	$249.00
Purchase #4	$224.85	4.180%	$234.2487	$234.25	$234.25	$234.20
Purchase #5	$12.54	11.600%	$13.9946	$13.99	$14.00	$14.00
Purchase #6	$212.72	4.379%	$222.035	$222.04	$222.05	$222.00
Purchase #7	$103.33	6.102%	$109.6352	$109.64	$109.65	$109.60
7 purchase totals =	$951.41		$1,019.4984	$1,019.50	$1,019.55	$1,019.30