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	$239.84	10.842%	$265.8435	$265.84	$265.85	$265.80
Purchase #2	$234.31	9.187%	$255.8361	$255.84	$255.85	$255.80
Purchase #3	$130.73	10.525%	$144.4893	$144.49	$144.50	$144.50
Purchase #4	$169.81	10.476%	$187.5993	$187.60	$187.60	$187.60
Purchase #5	$97.55	11.567%	$108.8336	$108.83	$108.85	$108.80
Purchase #6	$200.32	12.593%	$225.5463	$225.55	$225.55	$225.50
Purchase #7	$91.61	3.807%	$95.0976	$95.10	$95.10	$95.10
7 purchase totals =	$1,164.17		$1,283.2457	$1,283.25	$1,283.30	$1,283.10