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	$47.98	9.272%	$52.4287	$52.43	$52.45	$52.40
Purchase #2	$134.35	10.451%	$148.3909	$148.39	$148.40	$148.40
Purchase #3	$44.39	9.321%	$48.5276	$48.53	$48.55	$48.50
Purchase #4	$134.54	12.163%	$150.9041	$150.90	$150.90	$150.90
Purchase #5	$35.64	5.421%	$37.572	$37.57	$37.55	$37.60
Purchase #6	$31.75	11.727%	$35.4733	$35.47	$35.45	$35.50
Purchase #7	$45.91	6.394%	$48.8455	$48.85	$48.85	$48.80
7 purchase totals =	$474.56		$522.1421	$522.14	$522.15	$522.10