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	$83.89	6.509%	$89.3504	$89.35	$89.35	$89.40
Purchase #2	$196.25	11.283%	$218.3929	$218.39	$218.40	$218.40
Purchase #3	$78.89	8.727%	$85.7747	$85.77	$85.75	$85.80
Purchase #4	$91.53	9.238%	$99.9855	$99.99	$100.00	$100.00
Purchase #5	$211.42	10.312%	$233.2216	$233.22	$233.20	$233.20
Purchase #6	$9.70	6.805%	$10.3601	$10.36	$10.35	$10.40
Purchase #7	$117.85	13.222%	$133.4321	$133.43	$133.45	$133.40
7 purchase totals =	$789.53		$870.5173	$870.51	$870.50	$870.60