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	$18.92	3.659%	$19.6123	$19.61	$19.60	$19.60
Purchase #2	$83.69	12.688%	$94.3086	$94.31	$94.30	$94.30
Purchase #3	$103.86	4.147%	$108.1671	$108.17	$108.15	$108.20
Purchase #4	$29.72	9.285%	$32.4795	$32.48	$32.50	$32.50
Purchase #5	$111.94	10.857%	$124.0933	$124.09	$124.10	$124.10
Purchase #6	$102.89	4.323%	$107.3379	$107.34	$107.35	$107.30
Purchase #7	$82.74	3.872%	$85.9437	$85.94	$85.95	$85.90
7 purchase totals =	$533.76		$571.9424	$571.94	$571.95	$571.90