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	$49.95	6.828%	$53.3606	$53.36	$53.35	$53.40
Purchase #2	$145.82	13.723%	$165.8309	$165.83	$165.85	$165.80
Purchase #3	$24.52	5.811%	$25.9449	$25.94	$25.95	$25.90
Purchase #4	$21.81	8.185%	$23.5951	$23.60	$23.60	$23.60
Purchase #5	$192.52	12.814%	$217.1895	$217.19	$217.20	$217.20
Purchase #6	$81.72	10.520%	$90.3169	$90.32	$90.30	$90.30
Purchase #7	$79.63	5.315%	$83.8623	$83.86	$83.85	$83.90
7 purchase totals =	$595.97		$660.1002	$660.10	$660.10	$660.10