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	$75.79	10.605%	$83.8275	$83.83	$83.85	$83.80
Purchase #2	$125.46	6.252%	$133.3038	$133.30	$133.30	$133.30
Purchase #3	$151.30	13.634%	$171.9282	$171.93	$171.95	$171.90
Purchase #4	$159.71	5.249%	$168.0932	$168.09	$168.10	$168.10
Purchase #5	$24.79	9.748%	$27.2065	$27.21	$27.20	$27.20
Purchase #6	$78.61	9.128%	$85.7855	$85.79	$85.80	$85.80
Purchase #7	$227.51	12.377%	$255.6689	$255.67	$255.65	$255.70
7 purchase totals =	$843.17		$925.8136	$925.82	$925.85	$925.80