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	$134.45	12.744%	$151.5843	$151.58	$151.60	$151.60
Purchase #2	$235.55	13.128%	$266.473	$266.47	$266.45	$266.50
Purchase #3	$129.71	5.622%	$137.0023	$137.00	$137.00	$137.00
Purchase #4	$87.30	8.527%	$94.7441	$94.74	$94.75	$94.70
Purchase #5	$94.69	7.858%	$102.1307	$102.13	$102.15	$102.10
Purchase #6	$116.83	12.722%	$131.6931	$131.69	$131.70	$131.70
Purchase #7	$39.42	7.214%	$42.2638	$42.26	$42.25	$42.30
7 purchase totals =	$837.95		$925.8913	$925.87	$925.90	$925.90