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	$10.28	9.375%	$11.2438	$11.24	$11.25	$11.20
Purchase #2	$205.62	8.137%	$222.3513	$222.35	$222.35	$222.40
Purchase #3	$99.89	11.590%	$111.4673	$111.47	$111.45	$111.50
Purchase #4	$31.28	11.639%	$34.9207	$34.92	$34.90	$34.90
Purchase #5	$10.47	9.724%	$11.4881	$11.49	$11.50	$11.50
Purchase #6	$137.52	6.266%	$146.137	$146.14	$146.15	$146.10
Purchase #7	$113.44	5.183%	$119.3196	$119.32	$119.30	$119.30
7 purchase totals =	$608.50		$656.9278	$656.93	$656.90	$656.90