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	$140.86	13.546%	$159.9409	$159.94	$159.95	$159.90
Purchase #2	$224.94	10.716%	$249.0446	$249.04	$249.05	$249.00
Purchase #3	$58.75	6.189%	$62.386	$62.39	$62.40	$62.40
Purchase #4	$81.29	11.385%	$90.5449	$90.54	$90.55	$90.50
Purchase #5	$169.98	5.142%	$178.7204	$178.72	$178.70	$178.70
Purchase #6	$85.91	9.297%	$93.8971	$93.90	$93.90	$93.90
Purchase #7	$82.41	3.845%	$85.5787	$85.58	$85.60	$85.60
7 purchase totals =	$844.14		$920.1126	$920.11	$920.15	$920.00