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	$73.97	10.703%	$81.887	$81.89	$81.90	$81.90
Purchase #2	$212.98	7.416%	$228.7746	$228.77	$228.75	$228.80
Purchase #3	$204.76	13.536%	$232.4763	$232.48	$232.50	$232.50
Purchase #4	$63.85	13.377%	$72.3912	$72.39	$72.40	$72.40
Purchase #5	$139.51	13.667%	$158.5768	$158.58	$158.60	$158.60
Purchase #6	$192.39	13.252%	$217.8855	$217.89	$217.90	$217.90
Purchase #7	$140.92	6.504%	$150.0854	$150.09	$150.10	$150.10
7 purchase totals =	$1,028.38		$1,142.0768	$1,142.09	$1,142.15	$1,142.20