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	$230.83	11.558%	$257.5093	$257.51	$257.50	$257.50
Purchase #2	$83.47	11.346%	$92.9405	$92.94	$92.95	$92.90
Purchase #3	$85.50	12.147%	$95.8857	$95.89	$95.90	$95.90
Purchase #4	$90.32	6.847%	$96.5042	$96.50	$96.50	$96.50
Purchase #5	$247.73	3.785%	$257.1066	$257.11	$257.10	$257.10
Purchase #6	$107.46	13.145%	$121.5856	$121.59	$121.60	$121.60
Purchase #7	$169.79	5.349%	$178.8721	$178.87	$178.85	$178.90
7 purchase totals =	$1,015.10		$1,100.4040	$1,100.41	$1,100.40	$1,100.40