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	$113.75	11.214%	$126.5059	$126.51	$126.50	$126.50
Purchase #2	$87.25	3.157%	$90.0045	$90.00	$90.00	$90.00
Purchase #3	$18.50	7.731%	$19.9302	$19.93	$19.95	$19.90
Purchase #4	$18.84	5.724%	$19.9184	$19.92	$19.90	$19.90
Purchase #5	$160.57	12.669%	$180.9126	$180.91	$180.90	$180.90
Purchase #6	$195.95	6.456%	$208.6005	$208.60	$208.60	$208.60
Purchase #7	$174.98	5.802%	$185.1323	$185.13	$185.15	$185.10
7 purchase totals =	$769.84		$831.0044	$831.00	$831.00	$830.90