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	$168.34	6.615%	$179.4757	$179.48	$179.50	$179.50
Purchase #2	$43.59	6.116%	$46.256	$46.26	$46.25	$46.30
Purchase #3	$71.33	10.558%	$78.861	$78.86	$78.85	$78.90
Purchase #4	$211.34	10.382%	$233.2813	$233.28	$233.30	$233.30
Purchase #5	$84.90	11.818%	$94.9335	$94.93	$94.95	$94.90
Purchase #6	$24.49	4.212%	$25.5215	$25.52	$25.50	$25.50
Purchase #7	$21.72	8.551%	$23.5773	$23.58	$23.60	$23.60
7 purchase totals =	$625.71		$681.9063	$681.91	$681.95	$682.00