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	$14.57	7.403%	$15.6486	$15.65	$15.65	$15.60
Purchase #2	$171.63	13.565%	$194.9116	$194.91	$194.90	$194.90
Purchase #3	$145.94	6.646%	$155.6392	$155.64	$155.65	$155.60
Purchase #4	$31.50	6.140%	$33.4341	$33.43	$33.45	$33.40
Purchase #5	$242.61	5.583%	$256.1549	$256.15	$256.15	$256.20
Purchase #6	$78.41	10.824%	$86.8971	$86.90	$86.90	$86.90
Purchase #7	$91.37	13.752%	$103.9352	$103.94	$103.95	$103.90
7 purchase totals =	$776.03		$846.6207	$846.62	$846.65	$846.50