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	$39.54	3.105%	$40.7677	$40.77	$40.75	$40.80
Purchase #2	$9.50	12.846%	$10.7204	$10.72	$10.70	$10.70
Purchase #3	$85.42	10.800%	$94.6454	$94.65	$94.65	$94.60
Purchase #4	$92.52	12.526%	$104.1091	$104.11	$104.10	$104.10
Purchase #5	$42.31	7.515%	$45.4896	$45.49	$45.50	$45.50
Purchase #6	$77.38	7.858%	$83.4605	$83.46	$83.45	$83.50
Purchase #7	$93.68	5.309%	$98.6535	$98.65	$98.65	$98.70
7 purchase totals =	$440.35		$477.8462	$477.85	$477.80	$477.90