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	$26.69	4.409%	$27.8668	$27.87	$27.85	$27.90
Purchase #2	$127.43	12.604%	$143.4913	$143.49	$143.50	$143.50
Purchase #3	$130.57	10.293%	$144.0096	$144.01	$144.00	$144.00
Purchase #4	$242.92	9.509%	$266.0193	$266.02	$266.00	$266.00
Purchase #5	$50.41	7.466%	$54.1736	$54.17	$54.15	$54.20
Purchase #6	$180.41	4.216%	$188.0161	$188.02	$188.00	$188.00
Purchase #7	$143.87	12.680%	$162.1127	$162.11	$162.10	$162.10
7 purchase totals =	$902.30		$985.6894	$985.69	$985.60	$985.70