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	$134.55	7.157%	$144.1797	$144.18	$144.20	$144.20
Purchase #2	$59.35	4.247%	$61.8706	$61.87	$61.85	$61.90
Purchase #3	$219.30	10.127%	$241.5085	$241.51	$241.50	$241.50
Purchase #4	$249.96	8.614%	$271.4916	$271.49	$271.50	$271.50
Purchase #5	$228.75	3.710%	$237.2366	$237.24	$237.25	$237.20
Purchase #6	$131.90	6.456%	$140.4155	$140.42	$140.40	$140.40
Purchase #7	$134.56	10.617%	$148.8462	$148.85	$148.85	$148.80
7 purchase totals =	$1,158.37		$1,245.5487	$1,245.56	$1,245.55	$1,245.50