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	$71.92	9.711%	$78.9042	$78.90	$78.90	$78.90
Purchase #2	$149.94	12.492%	$168.6705	$168.67	$168.65	$168.70
Purchase #3	$134.82	9.166%	$147.1776	$147.18	$147.20	$147.20
Purchase #4	$79.95	3.330%	$82.6123	$82.61	$82.60	$82.60
Purchase #5	$143.47	3.729%	$148.82	$148.82	$148.80	$148.80
Purchase #6	$241.69	4.694%	$253.0349	$253.03	$253.05	$253.00
Purchase #7	$164.85	8.509%	$178.8771	$178.88	$178.90	$178.90
7 purchase totals =	$986.64		$1,058.0966	$1,058.09	$1,058.10	$1,058.10