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	$125.87	11.196%	$139.9624	$139.96	$139.95	$140.00
Purchase #2	$248.84	13.130%	$281.5127	$281.51	$281.50	$281.50
Purchase #3	$118.72	8.335%	$128.6153	$128.62	$128.60	$128.60
Purchase #4	$102.33	11.338%	$113.9322	$113.93	$113.95	$113.90
Purchase #5	$28.64	13.254%	$32.4359	$32.44	$32.45	$32.40
Purchase #6	$119.61	10.596%	$132.2839	$132.28	$132.30	$132.30
Purchase #7	$21.88	10.803%	$24.2437	$24.24	$24.25	$24.20
7 purchase totals =	$765.89		$852.9861	$852.98	$853.00	$852.90