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	$247.42	11.357%	$275.5195	$275.52	$275.50	$275.50
Purchase #2	$34.83	12.294%	$39.112	$39.11	$39.10	$39.10
Purchase #3	$18.43	13.782%	$20.97	$20.97	$20.95	$21.00
Purchase #4	$198.51	3.182%	$204.8266	$204.83	$204.85	$204.80
Purchase #5	$106.80	6.720%	$113.977	$113.98	$114.00	$114.00
Purchase #6	$102.48	9.772%	$112.4943	$112.49	$112.50	$112.50
Purchase #7	$96.45	13.565%	$109.5334	$109.53	$109.55	$109.50
7 purchase totals =	$804.92		$876.4328	$876.43	$876.45	$876.40