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	$31.61	4.342%	$32.9825	$32.98	$33.00	$33.00
Purchase #2	$48.54	11.495%	$54.1197	$54.12	$54.10	$54.10
Purchase #3	$192.76	11.648%	$215.2127	$215.21	$215.20	$215.20
Purchase #4	$131.87	12.284%	$148.0689	$148.07	$148.05	$148.10
Purchase #5	$132.85	7.447%	$142.7433	$142.74	$142.75	$142.70
Purchase #6	$164.69	11.621%	$183.8286	$183.83	$183.85	$183.80
Purchase #7	$150.85	5.387%	$158.9763	$158.98	$159.00	$159.00
7 purchase totals =	$853.17		$935.9320	$935.93	$935.95	$935.90