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	$224.55	6.815%	$239.8531	$239.85	$239.85	$239.90
Purchase #2	$164.60	5.128%	$173.0407	$173.04	$173.05	$173.00
Purchase #3	$168.42	7.309%	$180.7298	$180.73	$180.75	$180.70
Purchase #4	$188.77	9.566%	$206.8277	$206.83	$206.85	$206.80
Purchase #5	$85.47	5.105%	$89.8332	$89.83	$89.85	$89.80
Purchase #6	$96.29	9.569%	$105.504	$105.50	$105.50	$105.50
Purchase #7	$234.34	5.569%	$247.3904	$247.39	$247.40	$247.40
7 purchase totals =	$1,162.44		$1,243.1789	$1,243.17	$1,243.25	$1,243.10