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	$40.93	3.478%	$42.3535	$42.35	$42.35	$42.40
Purchase #2	$16.25	9.744%	$17.8334	$17.83	$17.85	$17.80
Purchase #3	$16.99	5.866%	$17.9866	$17.99	$18.00	$18.00
Purchase #4	$151.83	10.309%	$167.4822	$167.48	$167.50	$167.50
Purchase #5	$45.29	6.855%	$48.3946	$48.39	$48.40	$48.40
Purchase #6	$200.35	7.790%	$215.9573	$215.96	$215.95	$216.00
Purchase #7	$98.98	12.605%	$111.4564	$111.46	$111.45	$111.50
7 purchase totals =	$570.62		$621.4640	$621.46	$621.50	$621.60