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	$16.64	8.644%	$18.0784	$18.08	$18.10	$18.10
Purchase #2	$228.81	11.556%	$255.2513	$255.25	$255.25	$255.30
Purchase #3	$175.42	3.603%	$181.7404	$181.74	$181.75	$181.70
Purchase #4	$221.98	4.319%	$231.5673	$231.57	$231.55	$231.60
Purchase #5	$203.93	9.268%	$222.8302	$222.83	$222.85	$222.80
Purchase #6	$72.42	10.556%	$80.0647	$80.06	$80.05	$80.10
Purchase #7	$53.42	12.788%	$60.2513	$60.25	$60.25	$60.30
7 purchase totals =	$972.62		$1,049.7836	$1,049.78	$1,049.80	$1,049.90