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	$78.66	13.723%	$89.4545	$89.45	$89.45	$89.50
Purchase #2	$157.82	7.363%	$169.4403	$169.44	$169.45	$169.40
Purchase #3	$63.42	10.381%	$70.0036	$70.00	$70.00	$70.00
Purchase #4	$101.83	3.183%	$105.0712	$105.07	$105.05	$105.10
Purchase #5	$145.32	6.514%	$154.7861	$154.79	$154.80	$154.80
Purchase #6	$52.72	10.651%	$58.3352	$58.34	$58.35	$58.30
Purchase #7	$177.50	4.641%	$185.7378	$185.74	$185.75	$185.70
7 purchase totals =	$777.27		$832.8287	$832.83	$832.85	$832.80