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	$132.70	9.270%	$145.0013	$145.00	$145.00	$145.00
Purchase #2	$56.71	5.544%	$59.854	$59.85	$59.85	$59.90
Purchase #3	$93.80	7.245%	$100.5958	$100.60	$100.60	$100.60
Purchase #4	$193.40	8.485%	$209.81	$209.81	$209.80	$209.80
Purchase #5	$37.39	5.206%	$39.3365	$39.34	$39.35	$39.30
Purchase #6	$229.61	12.793%	$258.984	$258.98	$259.00	$259.00
Purchase #7	$168.61	4.105%	$175.5314	$175.53	$175.55	$175.50
7 purchase totals =	$912.22		$989.1130	$989.11	$989.15	$989.10