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	$250.45	8.513%	$271.7708	$271.77	$271.75	$271.80
Purchase #2	$49.99	4.453%	$52.2161	$52.22	$52.20	$52.20
Purchase #3	$78.78	13.423%	$89.3546	$89.35	$89.35	$89.40
Purchase #4	$102.49	5.184%	$107.8031	$107.80	$107.80	$107.80
Purchase #5	$25.61	7.357%	$27.4941	$27.49	$27.50	$27.50
Purchase #6	$164.52	12.741%	$185.4815	$185.48	$185.50	$185.50
Purchase #7	$95.40	6.667%	$101.7603	$101.76	$101.75	$101.80
7 purchase totals =	$767.24		$835.8805	$835.87	$835.85	$836.00