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	$129.85	9.429%	$142.0936	$142.09	$142.10	$142.10
Purchase #2	$236.64	12.773%	$266.866	$266.87	$266.85	$266.90
Purchase #3	$87.53	7.841%	$94.3932	$94.39	$94.40	$94.40
Purchase #4	$172.54	10.381%	$190.4514	$190.45	$190.45	$190.50
Purchase #5	$47.89	5.421%	$50.4861	$50.49	$50.50	$50.50
Purchase #6	$26.70	7.544%	$28.7142	$28.71	$28.70	$28.70
Purchase #7	$67.88	5.665%	$71.7254	$71.73	$71.75	$71.70
7 purchase totals =	$769.03		$844.7299	$844.73	$844.75	$844.80