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	$227.55	12.655%	$256.3465	$256.35	$256.35	$256.30
Purchase #2	$165.67	4.158%	$172.5586	$172.56	$172.55	$172.60
Purchase #3	$32.79	4.722%	$34.3383	$34.34	$34.35	$34.30
Purchase #4	$152.74	8.247%	$165.3365	$165.34	$165.35	$165.30
Purchase #5	$175.69	11.465%	$195.8329	$195.83	$195.85	$195.80
Purchase #6	$82.90	8.477%	$89.9274	$89.93	$89.95	$89.90
Purchase #7	$69.60	10.661%	$77.0201	$77.02	$77.00	$77.00
7 purchase totals =	$906.94		$991.3603	$991.37	$991.40	$991.20