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	$96.70	6.606%	$103.088	$103.09	$103.10	$103.10
Purchase #2	$174.31	4.316%	$181.8332	$181.83	$181.85	$181.80
Purchase #3	$155.44	10.339%	$171.5109	$171.51	$171.50	$171.50
Purchase #4	$60.93	7.754%	$65.6545	$65.65	$65.65	$65.70
Purchase #5	$92.79	12.662%	$104.5391	$104.54	$104.55	$104.50
Purchase #6	$64.45	3.128%	$66.466	$66.47	$66.45	$66.50
Purchase #7	$153.65	3.723%	$159.3704	$159.37	$159.35	$159.40
7 purchase totals =	$798.27		$852.4621	$852.46	$852.45	$852.50