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	$133.72	4.348%	$139.5341	$139.53	$139.55	$139.50
Purchase #2	$106.87	5.189%	$112.4155	$112.42	$112.40	$112.40
Purchase #3	$148.96	8.846%	$162.137	$162.14	$162.15	$162.10
Purchase #4	$165.79	5.139%	$174.3099	$174.31	$174.30	$174.30
Purchase #5	$102.53	8.631%	$111.3794	$111.38	$111.40	$111.40
Purchase #6	$87.82	10.277%	$96.8453	$96.85	$96.85	$96.80
Purchase #7	$187.68	6.844%	$200.5248	$200.52	$200.50	$200.50
7 purchase totals =	$933.37		$997.1460	$997.15	$997.15	$997.00