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	$92.95	7.582%	$99.9975	$100.00	$100.00	$100.00
Purchase #2	$51.53	5.683%	$54.4584	$54.46	$54.45	$54.50
Purchase #3	$94.46	9.632%	$103.5584	$103.56	$103.55	$103.60
Purchase #4	$95.92	3.337%	$99.1209	$99.12	$99.10	$99.10
Purchase #5	$139.81	5.692%	$147.768	$147.77	$147.75	$147.80
Purchase #6	$111.44	8.708%	$121.1442	$121.14	$121.15	$121.10
Purchase #7	$161.49	8.298%	$174.8904	$174.89	$174.90	$174.90
7 purchase totals =	$747.60		$800.9378	$800.94	$800.90	$801.00