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	$36.43	8.223%	$39.4256	$39.43	$39.45	$39.40
Purchase #2	$172.49	10.363%	$190.3651	$190.37	$190.35	$190.40
Purchase #3	$137.98	3.461%	$142.7555	$142.76	$142.75	$142.80
Purchase #4	$76.31	12.269%	$85.6725	$85.67	$85.65	$85.70
Purchase #5	$143.95	10.691%	$159.3397	$159.34	$159.35	$159.30
Purchase #6	$162.47	10.690%	$179.838	$179.84	$179.85	$179.80
Purchase #7	$160.68	3.856%	$166.8758	$166.88	$166.90	$166.90
7 purchase totals =	$890.31		$964.2722	$964.29	$964.30	$964.30