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	$49.25	10.264%	$54.305	$54.31	$54.30	$54.30
Purchase #2	$107.71	12.663%	$121.3493	$121.35	$121.35	$121.30
Purchase #3	$47.38	11.717%	$52.9315	$52.93	$52.95	$52.90
Purchase #4	$58.47	6.755%	$62.4196	$62.42	$62.40	$62.40
Purchase #5	$63.58	5.277%	$66.9351	$66.94	$66.95	$66.90
Purchase #6	$55.77	6.546%	$59.4207	$59.42	$59.40	$59.40
Purchase #7	$200.31	6.393%	$213.1158	$213.12	$213.10	$213.10
7 purchase totals =	$582.47		$630.4770	$630.49	$630.45	$630.30