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	$223.98	6.851%	$239.3249	$239.32	$239.30	$239.30
Purchase #2	$154.30	6.252%	$163.9468	$163.95	$163.95	$163.90
Purchase #3	$137.40	4.852%	$144.0666	$144.07	$144.05	$144.10
Purchase #4	$233.76	13.282%	$264.808	$264.81	$264.80	$264.80
Purchase #5	$105.98	5.227%	$111.5196	$111.52	$111.50	$111.50
Purchase #6	$68.51	7.386%	$73.5701	$73.57	$73.55	$73.60
Purchase #7	$73.54	6.461%	$78.2914	$78.29	$78.30	$78.30
7 purchase totals =	$997.47		$1,075.5274	$1,075.53	$1,075.45	$1,075.50