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	$138.34	7.439%	$148.6311	$148.63	$148.65	$148.60
Purchase #2	$38.68	13.403%	$43.8643	$43.86	$43.85	$43.90
Purchase #3	$49.63	11.736%	$55.4546	$55.45	$55.45	$55.50
Purchase #4	$71.83	10.379%	$79.2852	$79.29	$79.30	$79.30
Purchase #5	$130.92	7.760%	$141.0794	$141.08	$141.10	$141.10
Purchase #6	$159.75	12.414%	$179.5814	$179.58	$179.60	$179.60
Purchase #7	$123.49	7.254%	$132.448	$132.45	$132.45	$132.40
7 purchase totals =	$712.64		$780.3440	$780.34	$780.40	$780.40