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	$27.39	8.652%	$29.7598	$29.76	$29.75	$29.80
Purchase #2	$82.28	4.431%	$85.9258	$85.93	$85.95	$85.90
Purchase #3	$200.85	7.267%	$215.4458	$215.45	$215.45	$215.40
Purchase #4	$52.82	7.196%	$56.6209	$56.62	$56.60	$56.60
Purchase #5	$68.53	4.168%	$71.3863	$71.39	$71.40	$71.40
Purchase #6	$13.40	11.565%	$14.9497	$14.95	$14.95	$14.90
Purchase #7	$195.71	11.847%	$218.8958	$218.90	$218.90	$218.90
7 purchase totals =	$640.98		$692.9841	$693.00	$693.00	$692.90