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	$74.44	4.117%	$77.5047	$77.50	$77.50	$77.50
Purchase #2	$213.68	9.308%	$233.5693	$233.57	$233.55	$233.60
Purchase #3	$158.82	13.663%	$180.5196	$180.52	$180.50	$180.50
Purchase #4	$14.32	8.725%	$15.5694	$15.57	$15.55	$15.60
Purchase #5	$240.36	13.488%	$272.7798	$272.78	$272.80	$272.80
Purchase #6	$112.76	13.856%	$128.384	$128.38	$128.40	$128.40
Purchase #7	$99.45	5.615%	$105.0341	$105.03	$105.05	$105.00
7 purchase totals =	$913.83		$1,013.3609	$1,013.35	$1,013.35	$1,013.40