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	$20.52	11.702%	$22.9213	$22.92	$22.90	$22.90
Purchase #2	$127.25	3.119%	$131.2189	$131.22	$131.20	$131.20
Purchase #3	$76.82	9.217%	$83.9005	$83.90	$83.90	$83.90
Purchase #4	$90.71	4.189%	$94.5098	$94.51	$94.50	$94.50
Purchase #5	$8.71	6.851%	$9.3067	$9.31	$9.30	$9.30
Purchase #6	$39.61	13.131%	$44.8112	$44.81	$44.80	$44.80
Purchase #7	$119.95	11.181%	$133.3616	$133.36	$133.35	$133.40
7 purchase totals =	$483.57		$520.0300	$520.03	$519.95	$520.00