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	$123.31	12.766%	$139.0518	$139.05	$139.05	$139.10
Purchase #2	$40.28	11.754%	$45.0145	$45.01	$45.00	$45.00
Purchase #3	$10.70	5.457%	$11.2839	$11.28	$11.30	$11.30
Purchase #4	$98.58	12.289%	$110.6945	$110.69	$110.70	$110.70
Purchase #5	$197.45	3.863%	$205.0775	$205.08	$205.10	$205.10
Purchase #6	$45.84	3.179%	$47.2973	$47.30	$47.30	$47.30
Purchase #7	$102.92	8.256%	$111.4171	$111.42	$111.40	$111.40
7 purchase totals =	$619.08		$669.8366	$669.83	$669.85	$669.90