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	$125.26	11.415%	$139.5584	$139.56	$139.55	$139.60
Purchase #2	$159.80	3.772%	$165.8277	$165.83	$165.85	$165.80
Purchase #3	$138.25	12.500%	$155.5313	$155.53	$155.55	$155.50
Purchase #4	$9.51	8.434%	$10.3121	$10.31	$10.30	$10.30
Purchase #5	$42.46	3.348%	$43.8816	$43.88	$43.90	$43.90
Purchase #6	$127.53	12.753%	$143.7939	$143.79	$143.80	$143.80
Purchase #7	$180.28	9.615%	$197.6139	$197.61	$197.60	$197.60
7 purchase totals =	$783.09		$856.5189	$856.51	$856.55	$856.50