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	$100.69	7.368%	$108.1088	$108.11	$108.10	$108.10
Purchase #2	$146.43	11.244%	$162.8946	$162.89	$162.90	$162.90
Purchase #3	$147.84	13.698%	$168.0911	$168.09	$168.10	$168.10
Purchase #4	$228.74	11.701%	$255.5049	$255.50	$255.50	$255.50
Purchase #5	$17.93	10.682%	$19.8453	$19.85	$19.85	$19.80
Purchase #6	$17.71	7.223%	$18.9892	$18.99	$19.00	$19.00
Purchase #7	$58.97	6.761%	$62.957	$62.96	$62.95	$63.00
7 purchase totals =	$718.31		$796.3909	$796.39	$796.40	$796.40