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	$125.26	5.175%	$131.7422	$131.74	$131.75	$131.70
Purchase #2	$78.48	9.417%	$85.8705	$85.87	$85.85	$85.90
Purchase #3	$11.55	7.408%	$12.4056	$12.41	$12.40	$12.40
Purchase #4	$62.77	5.436%	$66.1822	$66.18	$66.20	$66.20
Purchase #5	$38.81	13.183%	$43.9263	$43.93	$43.95	$43.90
Purchase #6	$97.99	8.799%	$106.6121	$106.61	$106.60	$106.60
Purchase #7	$169.70	13.298%	$192.2667	$192.27	$192.25	$192.30
7 purchase totals =	$584.56		$639.0056	$639.01	$639.00	$639.00