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	$14.40	4.247%	$15.0116	$15.01	$15.00	$15.00
Purchase #2	$134.85	10.160%	$148.5508	$148.55	$148.55	$148.60
Purchase #3	$87.41	13.671%	$99.3598	$99.36	$99.35	$99.40
Purchase #4	$127.53	7.468%	$137.0539	$137.05	$137.05	$137.10
Purchase #5	$38.94	12.704%	$43.8869	$43.89	$43.90	$43.90
Purchase #6	$32.56	3.390%	$33.6638	$33.66	$33.65	$33.70
Purchase #7	$241.72	10.265%	$266.5326	$266.53	$266.55	$266.50
7 purchase totals =	$677.41		$744.0594	$744.05	$744.05	$744.20