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	$85.84	8.617%	$93.2368	$93.24	$93.25	$93.20
Purchase #2	$77.77	12.421%	$87.4298	$87.43	$87.45	$87.40
Purchase #3	$133.62	7.406%	$143.5159	$143.52	$143.50	$143.50
Purchase #4	$70.29	4.667%	$73.5704	$73.57	$73.55	$73.60
Purchase #5	$82.30	8.706%	$89.465	$89.47	$89.45	$89.50
Purchase #6	$42.35	11.730%	$47.3177	$47.32	$47.30	$47.30
Purchase #7	$93.74	11.874%	$104.8707	$104.87	$104.85	$104.90
7 purchase totals =	$585.91		$639.4063	$639.42	$639.35	$639.40