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	$138.45	12.493%	$155.7466	$155.75	$155.75	$155.70
Purchase #2	$34.80	11.570%	$38.8264	$38.83	$38.85	$38.80
Purchase #3	$78.95	5.169%	$83.0309	$83.03	$83.05	$83.00
Purchase #4	$175.37	8.614%	$190.4764	$190.48	$190.50	$190.50
Purchase #5	$53.51	6.325%	$56.8945	$56.89	$56.90	$56.90
Purchase #6	$169.40	7.461%	$182.0389	$182.04	$182.05	$182.00
Purchase #7	$114.92	13.545%	$130.4859	$130.49	$130.50	$130.50
7 purchase totals =	$765.40		$837.4996	$837.51	$837.60	$837.40