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	$132.63	6.764%	$141.6011	$141.60	$141.60	$141.60
Purchase #2	$64.43	6.318%	$68.5007	$68.50	$68.50	$68.50
Purchase #3	$89.26	11.704%	$99.707	$99.71	$99.70	$99.70
Purchase #4	$243.65	5.647%	$257.4089	$257.41	$257.40	$257.40
Purchase #5	$45.78	13.225%	$51.8344	$51.83	$51.85	$51.80
Purchase #6	$42.64	9.436%	$46.6635	$46.66	$46.65	$46.70
Purchase #7	$162.46	9.800%	$178.3811	$178.38	$178.40	$178.40
7 purchase totals =	$780.85		$844.0967	$844.09	$844.10	$844.10