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	$208.88	3.300%	$215.773	$215.77	$215.75	$215.80
Purchase #2	$180.54	5.737%	$190.8976	$190.90	$190.90	$190.90
Purchase #3	$211.76	11.376%	$235.8498	$235.85	$235.85	$235.80
Purchase #4	$231.97	6.273%	$246.5215	$246.52	$246.50	$246.50
Purchase #5	$172.82	3.391%	$178.6803	$178.68	$178.70	$178.70
Purchase #6	$92.31	9.180%	$100.7841	$100.78	$100.80	$100.80
Purchase #7	$95.85	13.820%	$109.0965	$109.10	$109.10	$109.10
7 purchase totals =	$1,194.13		$1,277.6028	$1,277.60	$1,277.60	$1,277.60