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	$156.25	7.576%	$168.0875	$168.09	$168.10	$168.10
Purchase #2	$51.52	6.563%	$54.9013	$54.90	$54.90	$54.90
Purchase #3	$215.85	10.510%	$238.5358	$238.54	$238.55	$238.50
Purchase #4	$220.40	5.651%	$232.8548	$232.85	$232.85	$232.90
Purchase #5	$234.74	12.664%	$264.4675	$264.47	$264.45	$264.50
Purchase #6	$127.86	11.110%	$142.0652	$142.07	$142.05	$142.10
Purchase #7	$206.57	8.181%	$223.4695	$223.47	$223.45	$223.50
7 purchase totals =	$1,213.19		$1,324.3816	$1,324.39	$1,324.35	$1,324.50