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	$47.81	10.545%	$52.8516	$52.85	$52.85	$52.90
Purchase #2	$52.61	11.237%	$58.5218	$58.52	$58.50	$58.50
Purchase #3	$190.47	12.107%	$213.5302	$213.53	$213.55	$213.50
Purchase #4	$148.87	5.422%	$156.9417	$156.94	$156.95	$156.90
Purchase #5	$50.79	3.393%	$52.5133	$52.51	$52.50	$52.50
Purchase #6	$81.46	11.689%	$90.9819	$90.98	$91.00	$91.00
Purchase #7	$118.34	12.475%	$133.1029	$133.10	$133.10	$133.10
7 purchase totals =	$690.35		$758.4434	$758.43	$758.45	$758.40