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	$241.37	6.404%	$256.8273	$256.83	$256.85	$256.80
Purchase #2	$141.82	11.553%	$158.2045	$158.20	$158.20	$158.20
Purchase #3	$155.87	4.511%	$162.9013	$162.90	$162.90	$162.90
Purchase #4	$242.32	12.139%	$271.7352	$271.74	$271.75	$271.70
Purchase #5	$23.88	12.439%	$26.8504	$26.85	$26.85	$26.90
Purchase #6	$153.88	12.379%	$172.9288	$172.93	$172.95	$172.90
Purchase #7	$86.29	13.477%	$97.9193	$97.92	$97.90	$97.90
7 purchase totals =	$1,045.43		$1,147.3668	$1,147.37	$1,147.40	$1,147.30