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	$121.49	8.578%	$131.9114	$131.91	$131.90	$131.90
Purchase #2	$94.50	12.250%	$106.0763	$106.08	$106.10	$106.10
Purchase #3	$135.87	11.793%	$151.8931	$151.89	$151.90	$151.90
Purchase #4	$101.53	12.547%	$114.269	$114.27	$114.25	$114.30
Purchase #5	$78.93	11.509%	$88.0141	$88.01	$88.00	$88.00
Purchase #6	$241.39	5.697%	$255.142	$255.14	$255.15	$255.10
Purchase #7	$121.71	12.564%	$137.0016	$137.00	$137.00	$137.00
7 purchase totals =	$895.42		$984.3075	$984.30	$984.30	$984.30