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	$75.69	6.422%	$80.5508	$80.55	$80.55	$80.60
Purchase #2	$20.27	10.504%	$22.3992	$22.40	$22.40	$22.40
Purchase #3	$74.67	13.858%	$85.0178	$85.02	$85.00	$85.00
Purchase #4	$168.92	6.467%	$179.8441	$179.84	$179.85	$179.80
Purchase #5	$38.50	3.575%	$39.8764	$39.88	$39.90	$39.90
Purchase #6	$100.46	8.335%	$108.8333	$108.83	$108.85	$108.80
Purchase #7	$175.27	9.280%	$191.5351	$191.54	$191.55	$191.50
7 purchase totals =	$653.78		$708.0567	$708.06	$708.10	$708.00