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	$34.84	6.435%	$37.082	$37.08	$37.10	$37.10
Purchase #2	$182.32	10.169%	$200.8601	$200.86	$200.85	$200.90
Purchase #3	$77.98	10.438%	$86.1196	$86.12	$86.10	$86.10
Purchase #4	$214.79	7.692%	$231.3116	$231.31	$231.30	$231.30
Purchase #5	$30.90	7.226%	$33.1328	$33.13	$33.15	$33.10
Purchase #6	$155.78	12.126%	$174.6699	$174.67	$174.65	$174.70
Purchase #7	$111.25	13.754%	$126.5513	$126.55	$126.55	$126.60
7 purchase totals =	$807.86		$889.7273	$889.72	$889.70	$889.80