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	$133.72	4.460%	$139.6839	$139.68	$139.70	$139.70
Purchase #2	$78.83	6.432%	$83.9003	$83.90	$83.90	$83.90
Purchase #3	$16.87	4.249%	$17.5868	$17.59	$17.60	$17.60
Purchase #4	$97.51	5.508%	$102.8809	$102.88	$102.90	$102.90
Purchase #5	$32.56	4.179%	$33.9207	$33.92	$33.90	$33.90
Purchase #6	$160.53	9.851%	$176.3438	$176.34	$176.35	$176.30
Purchase #7	$104.83	6.226%	$111.3567	$111.36	$111.35	$111.40
7 purchase totals =	$624.85		$665.6731	$665.67	$665.70	$665.70