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	$7.45	5.800%	$7.8821	$7.88	$7.90	$7.90
Purchase #2	$80.69	5.487%	$85.1175	$85.12	$85.10	$85.10
Purchase #3	$16.48	12.768%	$18.5842	$18.58	$18.60	$18.60
Purchase #4	$238.55	10.389%	$263.333	$263.33	$263.35	$263.30
Purchase #5	$27.25	13.699%	$30.983	$30.98	$31.00	$31.00
Purchase #6	$43.52	11.619%	$48.5766	$48.58	$48.60	$48.60
Purchase #7	$20.83	10.119%	$22.9378	$22.94	$22.95	$22.90
7 purchase totals =	$434.77		$477.4142	$477.41	$477.50	$477.40