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	$143.81	10.483%	$158.8856	$158.89	$158.90	$158.90
Purchase #2	$234.90	13.852%	$267.4383	$267.44	$267.45	$267.40
Purchase #3	$48.47	3.367%	$50.102	$50.10	$50.10	$50.10
Purchase #4	$70.73	12.526%	$79.5896	$79.59	$79.60	$79.60
Purchase #5	$172.78	10.188%	$190.3828	$190.38	$190.40	$190.40
Purchase #6	$54.69	5.673%	$57.7926	$57.79	$57.80	$57.80
Purchase #7	$21.51	9.425%	$23.5373	$23.54	$23.55	$23.50
7 purchase totals =	$746.89		$827.7282	$827.73	$827.80	$827.70