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	$59.41	11.452%	$66.2136	$66.21	$66.20	$66.20
Purchase #2	$171.72	11.148%	$190.8633	$190.86	$190.85	$190.90
Purchase #3	$125.75	5.648%	$132.8524	$132.85	$132.85	$132.90
Purchase #4	$69.39	7.436%	$74.5498	$74.55	$74.55	$74.50
Purchase #5	$184.37	8.580%	$200.1889	$200.19	$200.20	$200.20
Purchase #6	$93.37	13.510%	$105.9843	$105.98	$106.00	$106.00
Purchase #7	$164.34	4.867%	$172.3384	$172.34	$172.35	$172.30
7 purchase totals =	$868.35		$942.9907	$942.98	$943.00	$943.00