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	$171.93	4.203%	$179.1562	$179.16	$179.15	$179.20
Purchase #2	$68.95	13.261%	$78.0935	$78.09	$78.10	$78.10
Purchase #3	$54.87	12.192%	$61.5598	$61.56	$61.55	$61.60
Purchase #4	$36.64	6.668%	$39.0832	$39.08	$39.10	$39.10
Purchase #5	$77.34	6.791%	$82.5922	$82.59	$82.60	$82.60
Purchase #6	$107.96	8.336%	$116.9595	$116.96	$116.95	$117.00
Purchase #7	$185.54	10.571%	$205.1534	$205.15	$205.15	$205.20
7 purchase totals =	$703.23		$762.5978	$762.59	$762.60	$762.80